What you can and can't claim in a property ad

"Guaranteed 8% rental yield." "Five minutes to the station." "1,100 sq ft of living space." Every one of those is checkable, and when someone checks, the only question that matters is what evidence sat in your file before the ad went live. Not what you meant. Not what the vendor said on the phone. Regulators, portals and complainants all work backwards from the words to the paperwork, and a claim with no paperwork behind it is a misrepresentation whether or not a buyer lost money.

What substantiation means to the people who ask for it

In the UK the Advertising Standards Authority (ASA), the independent regulator of advertising across media, applies the CAP Code: advertisers must hold documentary evidence for objective claims before the ad appears, and produce it on request in days rather than months. The ASA has upheld complaints against property advertisers over unqualified yield promises, on the simple ground that a forecast is not evidence of itself (ASA rulings database).

The US reaches the same place through the Federal Trade Commission's reasonable basis doctrine: an objective claim needs support at the moment it is made, not assembled later under pressure. The National Association of Realtors Code of Ethics adds a member duty (Article 12) to present a true picture in advertising and marketing, which puts local board discipline in play alongside the FTC. Across the EU, the Unfair Commercial Practices Directive treats misleading statements and misleading omissions as the same kind of offence.

Two gates sit outside this lesson and you should assume both: the anti-discrimination and fair-treatment rules the fair-treatment lesson sets out, and the mandatory pre-promotion disclosures covered in the disclosures lesson. What follows is narrower: can each claim in the copy be proved, by what document, dated when.

One second-order cost is worth knowing before you write anything. An upheld ASA ruling is published and stays searchable under the advertiser's name. The fine is often nothing; the permanent search result naming your brokerage is the real price.

"Guaranteed" anything

Yield, capital growth, occupancy: none can be guaranteed unless a contract actually backs the guarantee, for example a developer paying a fixed rent for the first 24 months as a term of the sale. Then the evidence is the clause, and the copy must carry the term with it, because "guaranteed rent" floating free of "for 24 months" is the misleading part.

Watch the arithmetic too, because "gross" does a lot of quiet work. A £250,000 flat let at £1,250 a month grosses £15,000, or 6%. Take off letting fees at 10% (£1,500), a £1,600 service charge, £350 ground rent, insurance and three weeks of void between tenancies (about £865), and the owner nets roughly £10,700, just over 4%. Advertising 6% is defensible if you say gross and show the comparables. Advertising 6% as "your return" is not.

Rewrite example:

• ❌ "Guaranteed 7% rental yield"
• ✅ "Estimated gross yield of 6 to 7%, based on comparable lettings in the postcode as of March 2026 (source: [agency name] rental data). Gross figure, before management fees, service charge and voids."

A failure mode specific to guaranteed-yield stock: the guarantee is usually funded out of an inflated purchase price. The buyer's lender down-values, the mortgage shortfall kills the sale, and the complaint that follows points straight at the marketing copy.

Distance and time claims

State the method or do not state the number. Brochure walk times are usually machine estimates at around 5 km/h with no crossings, no hills and no step-free routing, and they are frequently measured from a postcode centroid rather than the front door of the building being sold. On a large development those two points can be several hundred metres apart.

Rewrite example:

• ❌ "5 minutes to Clapham Junction"
• ✅ "0.4 miles from the main entrance, roughly an 8-minute walk at average pace (mapping software walking route, checked March 2026)"

Size, and the price claim resting on it

A floor area is a measurement, so name the basis. RICS Property Measurement and the IPMS standards distinguish gross internal from net internal area, and the gap is not trivial: reusing an old brochure's 78 sq m when a measured net internal figure is 72 sq m overstates the flat by 8%, and every price per square foot claim built on it is wrong by the same margin. Common edge cases that inflate a headline number: a loft with restricted head height, an integral garage, a balcony, or a shared hallway counted as living space. "Plan not to scale, for illustrative purposes" protects the drawing, not the number in the headline.

Superlatives without basis

"Unbeatable location" is puffery and generally tolerated. The line is crossed the moment the phrase implies something checkable. "Best value in the area" is opinion; "cheapest price per square foot in SE15" is a factual claim needing the full dataset behind it at a stated date. Comparative claims also decay: yours can be true on Monday and false on Thursday when a cheaper listing appears, so either date-stamp it or drop it. "Award-winning" needs the award and the year, and the award needs to belong to the property or the agency, not to the architect's previous scheme.

Energy and sustainability wording

The certificates and figures that must appear on a listing are the disclosures lesson's territory. The claim question here is narrower: does the adjective match the rating you hold? "Highly efficient" over a D-rated Victorian conversion is the mismatch that gets challenged, and it is challenged easily, because the band is public. Two recurring traps: describing solar panels as giving "free electricity" when they sit under a rent-a-roof lease and the benefit belongs to the operator, and claiming "recently upgraded insulation" with no invoice or installer certificate in the file.

Rewrite example:

• ❌ "Eco-conscious new build"
• ✅ "EPC rating B, with solar panels and triple glazing"

Imagery makes claims as well as copy

Pictures are claims and get judged as claims. Renderings of unbuilt schemes need labelling as computer-generated images; virtual staging needs labelling as virtual staging; a twilight sky dropped over a grey afternoon is arguable, but digitally deleting the scaffolding next door or the pylon behind the garden is not. The commonest quiet failure is a photograph that was true when taken: a 2021 shot of an open view now blocked by a completed block, still running because nobody re-shot it. Drone framing carries the same risk when it implies land that is not in the title.

Keep the unedited original and the shoot date for anything published. If you cannot produce the original, you cannot defend the edit.

The evidence file behind the copy

Sequencing, ownership and sign-off belong to the pre-launch lesson. What belongs here is the file itself: one line per claim, and the file exists before publication, not after a complaint.

1. Every number has a named source and the date it was pulled: agency rental data, measured floor plan, mapping route, comparable sales.
2. Every forecast says it is a forecast and states its basis in the same sentence, not in a footnote a portal will strip out.
3. Area figures name the measurement basis and who measured.
4. Images are held in unedited form with shoot dates, and CGI or virtual staging labels live in the asset filename so the label survives a reformat by a third-party portal.
5. Comparative and superlative claims carry a review date, because they expire without anyone editing the ad.

CLAIM: "5 minutes to the tube"
EVIDENCE: none on file
STATUS: unverified
FIX: distance from main entrance + method + estimated walk time
DEADLINE: before MLS/portal upload

Where enforcement actually bites

Regulators rarely move on a single ad. Action follows patterns: the same claim repeated across a development's whole campaign, or a claim tied to real financial loss. An investor who bought on a "guaranteed yield" that never appeared has a far stronger case than a buyer irritated by a walk time, and their complaint can travel to a regulator, a professional body and a solicitor at once.

Before any of that, the platforms filter you. Meta, which sells the ad inventory housing campaigns run on, screens creative and copy before delivery, and the large portals run their own banned-word checks on words like "guaranteed". The cost of a rejection is rarely the rewrite. It is the launch window: portals sort by recency, so a listing pulled and re-uploaded loses its new-listing slot, and syndicated copies on aggregators keep the old claim visible for days after you have fixed the original.

🎬 [VIDEO: "How the ASA Regulates Advertising" - youtube.com/@ASA_UK - a short explainer from the UK's Advertising Standards Authority on how complaints are assessed and enforced, useful for understanding the regulatory mindset behind claim substantiation]

Key takeaways

• The test is not whether a claim is plausible but whether the evidence pre-dates the ad, with a named source and a date attached.
• "Guaranteed" is safe only when a contract clause backs it, and the copy must carry the term of that clause with it.
• Distances, walk times and floor areas need their method named: entrance or centroid, gross or net internal, measured by whom.
• Adjectives about energy or sustainability have to match the rating you already hold; solar panels under a lease are not "free electricity".
• Images are claims, so keep unedited originals and shoot dates, label CGI and virtual staging, and re-shoot when the surroundings change.
• Comparative claims decay on their own, so give every superlative a review date or drop it.