These checks are only ever warranted by the provider of the check if you pay for them, and even then they have a lot of get out clauses. It is best to pay for the check in case it throws up something. If it doesn't, there could still be something lurking. For example, if the vendor took out a chattel mortgage ('logbook loan') on the car that was not registered with HPI/Experian, the warranty on the info does not hold good and you could find you have paid him for something he has already mortgaged to someone else.