Real estate comparables: how your appraiser calibrates them — the method, not the black box

When an appraisal report concludes on a value, the reader's legitimate question — buyer, seller, heir, banker — is always the same: where does this figure come from? For the comparison method, the answer comes in five steps, each traceable, each verifiable. A report compliant with the RICS Red Bookstandards documents them all; a hasty “opinion of value” skips almost all of them. Here is what happens between the visit to the property and the concluded value.

1. Why comparison dominates in residential — and what it demands

In residential — apartments, villas, plots in villa zones — the market produces a continuous flow of transactions between individuals. The value of a property can therefore be observed more directly than through any financial calculation: if very similar properties have recently changed hands at known prices, those prices are the expression of the market. That is why the comparison method is the reference method for establishing the market value of a residential property, whereas capitalisation or DCF prevail for income-producing assets — we set out this articulation in our overview of estimation methods and their reliability.

But the method's strength is also its fragility: it is worth exactly what its comparables and adjustments are worth. Three failings ruin it:

• The convenience comparable — chosen because it suits the desired conclusion, not because it is relevant.
• The blind average — adding heterogeneous prices per square metre and dividing, without correcting any difference between the properties.
• The listing mistaken for a transaction — confusing a displayed price (a seller's aspiration) with a concluded price (a market fact).

The expert's entire discipline consists of neutralising these three failings through a methodical chain. Step by step.

2. Step 1 — Sourcing: three families of references, three levels of reliability

A comparable is not a floating figure: it is a sourced reference. In Morocco, the expert draws on three families, which are never placed on the same footing.

2.1 Actual transactions — the bedrock

The price actually recorded is the only piece of data that evidences a completed market agreement. Here the expert mobilises the land references from the ANCFCCecosystem (transfers registered on land titles), the transactions known directly through previous assignments in the area, and the sales reported by the professional network (notaries, fellow practitioners, managers). Two precautions apply: verifying that the declared price reflects the economic reality of the exchange, and verifying that the transaction was genuinely at arm's length — a sale between members of the same family, a distressed sale or a price including furniture are not market references usable as they stand.

2.2 Properties under mandate — the market in the making

Properties currently for sale through partner agencies inform on the supply competing with the property being valued: at what price can a buyer, today, find an equivalent property? A serious mandate, with an asking price worked on by the agent, is more robust data than a private listing — but it remains an asking price, not a concluded one. The expert treats it as a bound, never as proof.

2.3 Recent listings — an indicator to handle with caution

Published listings reflect sellers' aspirations, with all the optimism, built-in negotiation margin and sometimes embellished surface areas that entails. They remain useful: in volume, they sketch the upper range of the market and flag the properties that are not selling (a listing ageing online is information in itself). But a report that relied only on listings would not record the market — it would copy its shop windows. The expert uses them for corroboration, explicitly flagging their nature in the report.

3. Step 2 — Filtering: period, area, typology

Not all the references collected are of equal worth: before any adjustment, the expert discards those that are not comparable at all. Three successive filters:

• The period. A market moves. An old transaction may have been concluded under market conditions that no longer exist (rates, competing new-build supply, district dynamics). The expert favours recent references; if forced to go further back for lack of references, he says so, and accounts for the market's evolution between the reference date and the valuation date.
• The area. In residential real estate, value is hyper-local: two streets can separate two micro-markets (seafront vs second line, quiet villa sector vs busy artery, gated development vs open fabric). The right perimeter is not administrative, it is a substitution perimeter: the area in which a buyer of the property being valued would genuinely look for an alternative.
• The typology. An apartment is not compared with a villa, an office floor is not compared with a retail unit, a plot in an apartment-building zone is not compared with a plot in a villa zone. Within the same typology, the expert also watches the size class: a studio and a four-room apartment do not have the same unit price per square metre, even in the same building — comparing their prices per square metre without precaution introduces a structural bias.

At the end of the filtering, a tightened panel of genuinely comparable references remains. It is on this panel — and this panel only — that the adjustments begin.

4. Step 3 — The adjustments: correcting each difference, one by one

This is the technical heart of the method, and what distinguishes it from an average. No comparable is identical to the property being valued; adjusting consists of answering, difference by difference, one simple question: what would this comparable have been worth had it displayed the characteristic of the property being valued? The main adjustment items in residential:

• Surface area. First a verification: is the same surface area being discussed throughout (usable, habitable, weighted with terraces and ancillary spaces)? Then a size effect: at equal location, the unit price per square metre varies with total surface area — the expert corrects this effect rather than suffering it.
• Floor and accessibility. A high floor with a lift, a ground floor on the street, a top floor without a lift: the market treats them differently, and the adjustment depends on the local context (in a building without a lift, the hierarchy reverses).
• Exposure and light. Orientation, dual aspect, facing buildings, floor-plate depth: differences barely visible on paper, highly visible on a visit — hence the importance of the expert having seen the property, and knowing the comparables beyond a line in a table.
• Fittings. Standing of the condominium, lift, security, basement parking, integrated air conditioning, quality of the common areas: each gap in amenity between the comparable and the property being valued calls for a correction one way or the other.
• State of repair. Renovated, habitable as is, in need of refreshment, in need of restructuring: the adjustment relies on the objective cost of the works needed to bring the comparable to the level of the property being valued (or the reverse), not on an impression.
• View and immediate surroundings. Sea or golf view, direct overlooking, noise from a main road, proximity of value-enhancing or value-detracting facilities: elements that only knowledge of the field allows to be weighted honestly.
• Ancillary spaces and attached rights. Garage, cellar, private garden, convertible roof terrace, particular shares of common areas: they are valued separately rather than drowned in the price per square metre.

Two rules govern the exercise. Each adjustment must be made explicit: its direction (upwards or downwards on the comparable), its justification, and its order of magnitude as the local market reveals it. And an over-adjusted comparable is no longer a comparable: when the corrections pile up to the point of denaturing the reference, the expert downgrades or discards it rather than twisting it. A transparent report shows these adjustments; an opaque report displays “retained” prices per square metre without ever saying why.

5. Step 4 — The ranking: 1st, 2nd and 3rd belt comparables

Not all the comparables surviving the filtering and the adjustments carry the same weight in the conclusion. Professional practice organises them into belts of proximity:

• First belt — the guiding references. Same micro-area, same typology, same size class, recent period, limited adjustments. Ideally actual transactions. These set the core of the range; a few solid first-belt references are worth more than a long, motley list.
• Second belt — the corroborating references. Offset on one or two criteria (a comparable adjoining area, a neighbouring typology, a slightly older reference), they require larger adjustments. They serve to confirm that the core of the range is consistent with the surrounding market.
• Third belt — the framing references. Further removed still, they set nothing: they bound. They make it possible to check that the concluded value does not stray outside the plausible envelope of the wider sector, and to document the reasoning when the local market is shallow.

This ranking has one decisive virtue: it prevents an atypical reference — the exceptionally high transaction of an exceptional property, or the knock-down sale of a hurried estate — from mechanically pulling the conclusion. The atypical is identified, explained, and weighted accordingly.

6. Step 5 — The synthesis: from the adjusted panel to the concluded value

Once the comparables are adjusted and ranked, the expert does not “take the average”: he concludes. The synthesis consists of drawing from the panel a tightened range, driven by the guiding references and corroborated by the following belts, then positioning the property being valued within that range according to its own characteristics — residual strengths and weaknesses that the adjustments have brought to light. The report then states:

• the concluded value, attached to its basis of value (most often market value — see our guide to the RICS Red Book bases of value);
• the valuation date — a value is always dated, never eternal;
• the assumptions retained and their limits (declared surface areas not measured, legal situation assumed regular, etc.);
• where appropriate, the cross-check with a second method — capitalisation of the market rent for a rented property, the cost approach for a specific building. When two independent methods converge, the conclusion gains robustness; when they diverge, the gap is explained — that is the whole point of the articulation between market value, rental value and reinstatement value.

It is this deliverable — sourced comparables, explicit adjustments, assumed weighting, dated conclusion — that makes an independent appraisal a reasoned basis for an amicable negotiation: discussing a purchase price, defending a sale price, objectifying a family partition, documenting a bank file. (To be distinguished from the court-ordered expert appraisal, where it is the judge who appoints the expert within proceedings.)

7. The reader's checklist: six questions to ask of any comparables-based report

• Sources: does each comparable state its nature (transaction, mandate, listing), its date and its location?
• Filtering: are the references from the same substitution area, the same typology, the same size class?
• Adjustments: are the corrections made explicit item by item, with their direction and justification — or does the report jump from raw prices to the conclusion?
• Ranking: are the comparables weighted, the atypical references identified and handled?
• Basis and date: is the basis of value named, the valuation date set?
• Visit: was the property inspected by the signing expert — and does the report describe what was observed?

Six “yes” answers: you are holding an appraisal. Several “no” answers: you are holding an opinion of value — useful to get an idea, insufficient to commit a wealth decision.

ReaConsult is an independent property valuation firm in Morocco. Our RICS-certified experts produce reports compliant with the RICS Red Book standards for individuals, Moroccans living abroad, banks, developers and institutions. Find all our guides on the ReaConsult blog, or read the version française of this article.