I've never bought from a really posh dealers like Lexus/Merc/BMW so can't say if they're any better, but the others I've dealt with have almost all been lying bastards. The guy I bought my Lexus off in particular, he knew something about the expensive problems which I had to get fixed. But then I guess they get stitched up the other way, people trading knackered cars in etc. so they have some justification for being like that.
The only exception was my Gen 3 Hyundai Coupe, the car was a disappointment but the dealers were excellent to buy from, and their service department was also brilliant. It was Bramwells in Wigan but they have now closed.