12 Property Red Flags Every Buyer Should Check Before Making an Offer

Buying a home is one of the few large financial decisions people make with incomplete information and a deadline attached. The listing arrives first, the viewing feels persuasive, and the documents — the part that actually determines what you own — usually arrive last, if at all.

A red flag is not a reason to abandon a property. Some of the best purchases we have seen were properties with visible problems that were correctly understood and correctly priced. The point of due diligence is not to find a perfect property. It is to make sure you are not paying a perfect-property price for something else.

1. The built area does not match the official records

The single most common discrepancy in residential transactions is floor area. A listing advertises 238 m². The cadastral record shows 209 m². An architect measures 261 m². All three numbers can be produced honestly, because they are measuring different things under different conventions.

Why it matters: price per square metre, mortgage valuation, tax base and resale all depend on which figure a future buyer or bank accepts. What to request: the registry description, the cadastral record, floor plans, and any architect's measurement. Who confirms it: an architect or surveyor. Deal breaker? Almost never — but it frequently changes the price. We unpack this in detail in Why the square metres in a property listing may be wrong.

2. The plot area is inconsistent between sources

Plot discrepancies are less discussed than built area and often more consequential. A plot advertised at 812 m² may appear differently on the cadastral map, and the physical boundary — a wall, a hedge, a driveway — may not follow either line.

Boundary drift matters when you plan to build, extend, install a pool, or simply sell to a careful buyer. Request the registry plan, the cadastral plan and a topographic survey where the values differ. A surveyor or architect reconciles them. It is rarely fatal, but a plot that cannot be reconciled is a plot that will be questioned again at resale.

3. Additions or extensions that never reached the records

Extensions are the classic quiet problem: a converted garage, an enclosed terrace, a guest annexe, an extra bedroom that appears in photographs but not in the paperwork. The work may be well built and entirely usable. The question is whether it is legally recognised.

Unrecorded work can affect mortgage lending, insurance, future permits and the price a cautious buyer will pay. Ask for the building licence, the completion certificate and any regularisation documents. In some jurisdictions older works can be regularised or declared; in others they cannot. A local lawyer and an architect should tell you which situation applies before you sign anything.

4. Basements and lower-ground rooms presented as living space

Lower-ground floors are frequently marketed as bedrooms, gyms or cinema rooms while being recorded as storage or non-habitable space. That distinction affects habitable area, ventilation and light requirements, and sometimes the legality of sleeping accommodation.

It also affects damp risk. Below-grade rooms in Mediterranean properties are the most common location for waterproofing failures. Ask what the space is classified as, when it was converted, and whether tanking or drainage was installed. Check the fresh paint in the corners.

5. Pools, terraces and outbuildings with unclear documentation

A pool exists physically or it does not — that part is easy. Whether it appears in the cadastral record, was licensed, and complies with current setback and safety requirements is a separate matter entirely.

The same applies to pergolas, casitas, garages and covered terraces. Request the licence and, where relevant, the pool's technical documentation. If the pool is undocumented, ask your lawyer what the realistic path to regularisation is and what it costs. Then decide whether that cost belongs in your offer.

6. Missing building or occupancy documentation

Most jurisdictions require some form of completion or occupancy certificate confirming that a building was finished as approved and is fit to live in. When that document cannot be produced, there is usually a reason — sometimes trivially administrative, sometimes not.

Missing occupancy documentation can complicate utility connections, tourist rental registration, mortgage approval and resale. Request it early. If it does not exist, treat that as a live question rather than an oversight, and get a written answer before exchange.

7. Planning restrictions you only discover later

Two identical-looking plots can have completely different futures. Protected classifications, coastal boundaries, minimum plot sizes, height limits, buildability ratios and rural land designations all constrain what you may do — and sometimes what the current owner has already done.

If part of your reason for buying is a future extension, a pool, a guest house or a rental permit, verify the planning position before you offer, not after. A short consultation with a local architect is inexpensive relative to the assumption it replaces.

8. Water, drainage and flood exposure

Hillside plots on the Costa del Sol drain fast and sometimes violently. Watch for eroded channels beside the plot, silt marks on lower walls, patched retaining structures, and gardens that slope towards the house rather than away from it.

Ask where surface water goes in a storm, whether the property connects to mains drainage or a septic system, and whether the access road has flooded. Neighbours answer this question more candidly than listings do.

9. Structural warning signs

Not all cracks matter. Fine shrinkage cracking in render is normal. What deserves professional attention: diagonal cracking at window and door corners, stepped cracks in blockwork, doors and windows that no longer close square, sloping floors, movement in retaining walls, and rust staining that suggests corroding reinforcement.

A structural engineer or surveyor is the right person to judge severity. A photograph and an opinion are not a diagnosis. If a seller has recently repainted a single wall, ask what was underneath it.

10. Damp, waterproofing and roof condition

Flat roofs, roof terraces, planters against walls and below-ground rooms are the usual sources. The tells are musty smells in closed rooms, blistering paint at skirting level, staining on ceilings below terraces, and salt deposits on masonry.

Waterproofing repairs range from modest to substantial, and the cost depends heavily on what sits above the failed membrane. Terraces with expensive tiling cost far more to repair than bare ones. Price the realistic remedy, not the optimistic one.

11. Renovation requirements disguised as cosmetic updates

"Needs some modernising" can mean paint and a kitchen, or it can mean a full rewire, replumbing, new windows, new roof waterproofing and a pool refurbishment. The visual difference at a viewing is smaller than the financial difference.

Check the age and condition of the consumer unit and wiring, the boiler and hot water system, air conditioning units, window glazing and frames, and the pool plant. Then build a low, expected and high cost range rather than a single number — the method we set out in The true cost of buying a renovation property.

12. An asking price no evidence supports

The final red flag is the one buyers most often accept without question. An asking price is a hope, not a valuation. It may be based on a neighbour's asking price, an old peak, or an agent's optimism about a specific buyer profile.

Ask what comparable properties actually completed at, not what they were listed at. Adjust for condition, area, plot, orientation and legal status. If the asking price only works when every uncertainty resolves in the seller's favour, that is a pricing problem, not a due-diligence problem. See Asking price vs fair value.

How to use red flags in a negotiation

Findings only become useful when they are specific. "The property needs work" invites a shrug. "The cadastral record shows 209 m² against 238 m² advertised, the pool has no licence on file, and the roof terrace waterproofing is at the end of its life — here is our costed position" invites a conversation.

Evidence also protects you from the opposite mistake: talking yourself out of a good property because something looked alarming and nobody checked. Quantified risk is the difference between a discount and a dead deal.

This is exactly what BuyerWingman is built to do — gather the listing, documents, photographs and seller statements in one place, cross-check them, and separate what is verified from what is claimed, inferred or simply unknown.