Qualifying the source of information
For each observation, record the source, date and nature of the information. An asking price is an advertised price. It does not become a transaction price simply because several listings display the same value. Also verify that a property is not listed multiple times: counting duplicates creates a misleading impression of market supply.
The method in practice
Define a comparable before using it: same usage, relevant market segment, sufficiently close location, documented floor area, understandable condition and features. Separate asking price, known transaction price, and valuation opinion. A neighbour's listing provides an indication of competition, not proof of a sale amount. For each reference, write a sentence justifying its inclusion or exclusion. An older observation or one concerning a renovated property can remain informative provided its limitations are explained. Avoid multiplying references solely to make an average look more impressive: sample relevance precedes calculation.
Fictional example
Three listings using the same photos may correspond to a single property. Examine the features before counting them as three independent observations.
Date, source and nature of data accompany the figure.
Comparing defined floor areas
Before calculating per unit of floor area, ensure you understand the measurement used in each document or listing. Different designations are not interchangeable without verification. List ancillary rooms, outdoor spaces and parking separately where helpful to the client. An exact arithmetical calculation remains misleading if its underlying data is not comparable.
The method in practice
Clean up the table without erasing its uncertainties. Keep the original value, unit, source, and any correction. If a surface area includes different elements depending on the listing, do not immediately calculate a common unit price. Ask what each measurement covers. In a mock exercise, one offer includes a parking space and another offers it separately: add an "inclusions" row rather than deducting a universal parking premium. Quantified adjustments must have an explicit basis. Failing that, present a qualitative difference and state what information will enable it to be better measured.
Fictional example
An advertised floor area that includes an outdoor space cannot automatically be compared to another that presents it separately.
Validate units and scope prior to applying the formula.
Expressing a proportionate conclusion
First state what the observations document: the features and asking prices of selected offers at a given date. Then explain the differences and sample limitations. Do not turn a few listings into a representative index for the whole of Casablanca. Your commercial comparison can help select viewings while remaining insufficient for a market valuation.
The method in practice
Draft a short but balanced contradictory note: selected data, discarded references, provisional outcome, and information liable to alter it. Test your conclusion with a less favourable hypothesis. If a minor change in an unknown cost reverses the choice, the recommendation must state this. The client may decide to request a quote before negotiating. Your note must not hide discrepancies that undermine the proposed option. It must also distinguish selection advice from a formal valuation: explaining why a property better matches a requirement does not mean certifying its market value. Always specify the question your work is answering.
Fictional example
“Among these dated offers, A better meets the parking requirement; we still need to confirm service charges” is a useful, properly framed conclusion.
A small sample clarifies a specific choice; it does not describe an entire market.
Your practical application work
Prepare a grid for four mock listings, two of which might refer to the same flat. The floor areas are not all defined in the same way.
- My grid columns
- Checks prior to comparison
- The limitation I explain to the client