Are they worth it? £140 for the basic and £190 for the comprehensive. What do they really do? I don't know anything about buying second hand cars but I can kick a tyre, look for rust/leaks and spot a faulty bulb as well as the next person. Or do they do a more advanced investigation?
Any other advice about buying second hand and how not to get robbed by a dealer would be much appreciated.
I'm looking at something like a 1.4 diesel medium sized car maybe 5 or 6 years old. Ideally a Japanese car as they seem to have less trouble than others.

