well normally i'd say don't waste your time with any mk3 vr6, let alone a gti, because where i'm from thats the car to buy, beat the shit out of, and sell, but just do some research real quick. like the guy above me said check the rockers and strut towers for rust. see if he's done the timing chains, which is probably a negative considering it's only got 90k and he's hoping he can get away with selling it and not having to do it. throw 2800 at him and see what he says, if not forget it, that car's not worth it unless he's taken absolutely prime care of it. good luck man, you're looking at a super fun car to drive.
oh yea and vwvortex.com will be your best friend.