Last year, I purchased a wonderful "like new" pair of engineer boots on ebay--they were every bit as good as advertised, for $80 including shipping (regular $250+!). I have a high arch, and they took some breaking in; I concluded that the previous owner had the same problem and just didn't give them enough time.
Contemporary Frye sizing is a bit generous--perfect for wearing comfortably with socks (like Born or Ariat sizing on me). I wear a 9-9.5, and in modern Fryes, a 9 is perfect, even a bit loose. HOWEVER, truly vintage Frye boots (before about 1990, say) run half a size smaller. Contemporary western styles for women also run a bit smaller and narrower--so sight unseen, I would probably buy a 9.5, myself.
Do be sure you know what you are getting if you are buying online and can't return. View lots of pictures (including an inside-the-boot view, if possible), ask about smoke smells if that bothers you, and confirm a heel-to-toe measurement taken on the sole. Also be sure you know how the various styles feel (campus boots can be stiff and heavy, for example--love it or hate it!).
Fryes are wonderful boots that will give you many years of wear. Cobblers love them, too--they are designed to be reheeled and resoled, and they are pretty easy to refurbish and even dye.
