Due diligence on a house rarely goes wrong because of one dramatic oversight. More often it is a series of small shortcuts made under time pressure, each reasonable in the moment, that add up to a purchase made with less information than the buyer believed they had. The errors below come up again and again, and nearly all of them are easy to avoid with a little forward planning.

1. Relying on the vendor’s report. Reports supplied by vendors can be useful background, but they were commissioned by the person selling the house. They may be months old, may not cover the areas a buyer cares about most, and the buyer often has no contract with the inspector, which limits any recourse if something was missed. Some buyers check whether the author will readdress or update the document for them; others commission their own from scratch. Either way, a vendor report is best treated as a prompt for questions rather than an answer.
2. Booking the inspection too late. Leaving it until the last days of a condition period leaves no room for follow-up. If the inspector recommends that a specialist look at the roof, the drains or the wiring, there may be no time to arrange it before the condition date. Lining up an inspector as soon as an offer is accepted, or even before, keeps options open. Busy periods in the market can stretch booking times, so a provisional slot arranged early is often easier to move than a new one is to find.
3. Choosing purely on price or speed. Inspectors vary in experience and in the depth of their reporting. A quick visit with a tick-box checklist may meet a deadline but skip detail. Asking about qualifications, whether the report follows the national residential inspection standard, and whether the inspector actually climbs into the ceiling and crawls beneath the floor helps compare like with like.
4. Not attending the inspection. Being present, at least for the end of the visit, gives buyers the chance to see issues first-hand and ask questions while the inspector is still on site. Photos explain a lot, but standing under a stained ceiling explains more. It is also a good moment to ask how serious a finding is in practical terms, something a written report does not always convey.
5. Skimming the limitations. Every report has limits. Furnished rooms, locked areas, roofs too steep or fragile to walk and subfloors with no access all reduce what can be assessed. Buyers who read only the summary may assume parts of the house were checked when they were not. Where a key area was not accessed, it may be possible to ask the vendor to make it available for a return visit.
6. Treating the result as a pass or fail. Almost every house has defects, including new ones. The value lies in understanding which issues are routine maintenance, which are expensive, and which need further investigation. Rough quotes for the significant items turn a list of problems into figures that can inform a negotiation or a decision to move on. A house with twenty minor items may be a better buy than one with two serious ones.
7. Ignoring the paperwork. A physical inspection does not show whether past work was consented. Cross-checking findings against the LIM and the council property file can reveal unconsented additions, missing code compliance certificates or hazards on the site that change how the inspector’s comments should be read. A bedroom that turns out to be an unconsented garage conversion is a very different proposition from the one advertised.

None of these mistakes is unusual, and most come from the pressure of a busy market rather than carelessness. Building the inspection into the purchase timeline from the very beginning, rather than treating it as an afterthought once the offer is signed, prevents most of them.

There is a quieter error that sits behind several of these: falling for a house before the checks are done. Once a buyer has mentally arranged the furniture, there is a natural tendency to explain away unwelcome findings or to read a report looking for reassurance rather than information. Asking a friend or relative who has no emotional stake to read the findings as well can provide a useful counterweight, as can deciding in advance which kinds of problem would be deal-breakers.

It also helps to think about who else should look at the house. A good building report is one piece of a wider picture, alongside the LIM, a title search, legal advice and, where relevant, specialist testing for meth, asbestos or weathertightness. Read together, those pieces put buyers in a much stronger position to decide whether a house is right for them, and on what terms.

Lastly, keep everything. The report, the LIM, correspondence with the vendor and any quotes obtained during the condition period are useful long after settlement, both when planning maintenance and when the time eventually comes to sell.