When Checkbook’s undercover shoppers paid for 12 inspections we were astonished by how poorly many of them performed. Of the 28 problems we deemed any inspector should catch, as a group they caught them only half the time. But what really surprised us was how little work many inspectors bothered to do. For instance, few performed up-close inspections of the roof, several didn’t test all the windows, outlets, or fixtures, and the reports supplied by some were brief and cursory.

So, before you hire an inspector, ask what exactly they’ll do and how long it will take them to do it. You can often determine the thoroughness of inspectors’ work by looking at sample reports they should readily supply, if requested. Already have a concern about the home? Make sure your inspector will check it.

Also look at customer reviews from homeowners we surveyed—we receive very mixed reviews for them. Ask candidates about certifications they hold (in this industry, the available programs appear meaningful) and inquire about their backgrounds. This is a field where experience truly matters. And because we found big price differences among companies, and little relationship between work quality and fees, make sure you don’t overpay for an inspection.

If you’re buying a new home, definitely get an inspection. Inspectors and real estate agents we spoke with repeatedly warned that builders (and DIY remodelers) frequently create lots of defects.