The ebay horns are all something to be wary of. Stick to a horn, vintage or new, from a company with a reputation behind it.
"The big four" for new horns are Keilwerth, Selmer, Yamaha, and Yanagisawa, and you can alos get a good deal on those if you buy used. Other good modern horns include the Cannonballs, Antiguas, and the Jupiters, both which also get very good press.
There are also a large number of good vintage horns to consider, like Conn, King, Selmer, Beuscher, Martin, etc. Check out www.saxpics.com where Pete Hales has tons of pictures and history on all the different Vintage horn Companies and some of the new ones.
For instruments, Ebay is a crapshoot, and I recomend that beginners stay away from it, and stick to someone that specializes in instruments when getting a first horn.