Slightly different direction, but also worth looking at the relevant Honest John review for whichever car you are thinking about and look through the 'good/bad' section, which can be a bit of an eye opener!. Especially important if you are buying something outwith it's warranty but quite expensive and complex (as most modern cars are).

HPI is good, but be careful if you pre buy several checks, useful if you are looking seriously at a choice of vehicles.

I did that, batch of 3 if i recall, and for some reason the system told me i had used all my pre paid checks after 2.

HPI never did reply to my emails about this, most annoying that, things go wrong now and again that is not the issue, but failing to even acknowledge a customer is poor.

Autotrader offer almost the same checks, ISTR buying a batch of 5 previouly and used all but 1, but the time limit expires sooner hence choosing HPI for the longer period of validity instead recently, my mistake.

As said the guarantees offered are conditional on phyical checks (mainly chassis numbers and confirming reg document markings) being made by you the buyer, submitting onto the system before completing a purchase.