I think regardless of if you get it from ebay or anywhere else you need to be ultra streetwise....check it out fully (Take someone with mechanical nonse if you don't have any) and don't hand over 1 penny till your 100% happy with what your buying.

Finally by law for private or business sales your allowed to take it back within 28 days in the same condition for a full refund if your not happy, if they refuse you can take legal action.