That bike sure looks like the 1999 model to me, solid colors are old models. The newer ones had multi colors. Heres a 1999 model picture of a larger frame online. You can call Trek with the serial and they will tell you the year. Also there is some seial decoders online.
http://www.epinions.com/bike-Bicycle...rek_7500__1999
The auction photo looks good, but Unless its really mint $350 may be too much. I would tell the seller of the discrepancy and ask for some dough back maybe.