Reading Rental Comparables Honestly: The Habits That Distort Evidence

Comparable evidence is only as good as the discipline applied to it. These are the habits that quietly bend a comparables schedule towards the answer you wanted.

A comparables schedule is a set of transactions assembled to answer one question: what would this unit let for today. The schedule itself is neutral. What distorts it is the sequence in which it is built, because an investor who already has a number in mind will unconsciously select, weight and discard evidence until the schedule agrees. These are the specific habits that do the damage.

Why these keep happening

Selection happens before analysis, and selection is where the bias enters. By the time anyone looks at the arithmetic, the decisions that mattered have already been taken: which transactions were collected, which were set aside as unrepresentative, which district boundary was used and which time window was considered current. A schedule can be internally faultless and still be wrong because of what never reached it.

1. Collecting evidence after forming a view on rent

Once a number is in your head, every transaction above it looks representative and every transaction below it looks like a special case with an explanation. This is not dishonesty, it is how judgement works when the target is known in advance. The result is a schedule that documents a conclusion rather than one that produced it.

• Avoid it by: Define the search parameters in writing first: district boundary, unit type, size band, time window and condition range, then collect everything that falls inside them before looking at any figure.
• Proof it is closed: A dated search specification issued before collection, with a note of every transaction excluded and why.

What it costs you: An income assumption that nobody can challenge, because the evidence supporting it was selected to support it.

2. Excluding the low transactions as unrepresentative

Low transactions usually have a reason, and the reason is often the most important information in the schedule: the unit was in poor condition, the owner needed it let quickly, the floor was unpopular, or that unit type is harder to move than you assumed. Removing them removes exactly the data that describes the downside you are about to underwrite.

• Avoid it by: Keep every transaction inside the parameters and explain each outlier rather than deleting it, then decide whether its explanation applies to your unit.
• Proof it is closed: A schedule showing the full range with a one-line reason for each transaction at the extremes.

What it costs you: A base case built on the upper half of the evidence, with the lower half discarded as noise.

3. Mixing time periods without saying so

A contract signed two years ago describes a different market from one signed last month, yet both sit in the schedule looking equally authoritative. Where the letting market has moved, an old transaction either overstates or understates current achievable rent, and the direction is not obvious without knowing which way the market has gone.

• Avoid it by: Date every line, weight recent evidence more heavily, and state the time window you treated as current.
• Proof it is closed: A schedule sorted by date with the cut-off for current evidence stated at the top.

What it costs you: An assumption anchored to conditions that no longer exist, in either direction.

4. Treating the district as homogeneous

Within a single named district, rents can differ materially between a street on a main road and one three turns inside, between a block facing a park and one facing a service yard, and between the side served by a metro entrance and the side that is not. Averaging across the district name smooths away the specific locational facts that determine your unit's rent.

• Avoid it by: Plot the comparables, walk the routes between them and the subject, and discard or adjust anything whose micro-location is materially different.
• Proof it is closed: A map of the comparables against the subject, with a note on access, frontage and surroundings for each.

What it costs you: A rent assumption that describes an average address rather than the one you are buying.

5. Ignoring what was conceded to achieve the rent

A headline rent agreed with two months free, a fit-out contribution or an unusually short commitment is not the same rent as one agreed on standard terms. Schedules that record only the annual figure treat these as equivalent, which systematically overstates the market. The concession is rarely advertised and is often the first thing an owner omits when asked.

• Avoid it by: For every line, record lease length, rent-free period, contributions, break rights and who pays utilities, then convert to an effective rent before comparing.
• Proof it is closed: An effective rent column in the schedule showing the adjustment from headline for each transaction.

What it costs you: An overstatement of market rent that then flows into both the income line and the capitalised exit.

6. Using too few transactions and calling it evidence

Two or three transactions can support almost any conclusion, because the variation between individual deals is wide and each one reflects the particular circumstances of its parties. A thin schedule does not become stronger by being presented confidently, and it is the situation in which a plausible but wrong answer is most likely.

• Avoid it by: Widen the search parameters deliberately and in a stated way rather than drawing conclusions from a handful of lines, and show the resulting range rather than a single point.
• Proof it is closed: A schedule with enough lines to show a distribution, and a stated range rather than a single rent.

What it costs you: A decision taken on a sample too small to distinguish the market from the motivation of one tenant.

7. Forgetting that the subject has to be let by someone

Evidence describes what other units achieved with their marketing, their managers and their condition. Your unit will be let by your manager, at your specification, with your tolerance for void. A schedule that ignores the quality of the letting process attributes to the market what was actually achieved by effort.

• Avoid it by: Ask who let each comparable and how long it took, and check whether your intended arrangement matches that standard.
• Proof it is closed: Marketing duration recorded against each comparable, with your own assumed letting period stated.

What it costs you: A rent assumption that is achievable in principle and unachievable with the management arrangement actually in place.

A short check before you sign

• Search parameters were written down before any transaction was collected.
• Every excluded transaction is listed with the reason for exclusion.
• Each line carries a date and the schedule states what counts as current.
• Micro-location has been checked on the ground rather than by district name.
• Headline rents have been converted to effective rents using the recorded terms.
• The output is a range with a stated central view, not a single confident figure.

If it has already happened

If you suspect a schedule was built to justify a number, the fastest repair is to rebuild it blind: hand the search parameters to someone who does not know your target rent and ask them to collect everything that qualifies. Compare the two schedules and examine every transaction present in theirs and absent from yours. That exercise usually relocates the central view, and if it does not, you have an assumption you can defend to a lender, a partner or an accredited valuer. Market conditions shift, so repeat the exercise before any decision that depends on the rent rather than relying on a schedule prepared months earlier.

Domira builds the numbers on a Saudi property with you before you commit: rent and cost evidence, condition and capital expenditure, the appraisal and the sensitivities that decide whether the deal survives a bad year. The investment decision stays yours, and so does the advice of your licensed tax and legal advisers.