Two points. First, when you ring up, just say you were ringing about the car for sale. Do not specify what car. If they are a dealer pretending it is a private sale, they will usually have to ask you what car you mean. Cut the call, they are trying to shift a car that would fail a warranty.

Second, if you really have no clue, book one of the roadside rescue services to go with you when you are very interested in a particular car. They will know the common faults of all major makes like the backs of their hands. The problems they point out will provide a point of negotiation of the fee of them coming with you off the price.