In my opinion, this is the #1 mistake I see people make when buying something new or used - buying the wrong size. The right size is far more important to me than any other factor (other than safety).

If the seat is just adjusted to high, and lowering to parallel with the bars causes it to fit, then it fits well. If you need the seat to be noticeably higher or lower than the handlebars, I wouldn't get it. I bought a new bike in high school that was a little to big for me, thinking I would keep growing (and I didn't), and it was really nice when I bought a new slightly smaller bike.