I have purchased a lot of fairly expensive items off Ebay including bows. Like the previous posters stated - if you see something you're interested in, check the seller's feedback. Another thing is to pay via Paypal. Your purchase is protected from fraud.
Just FYI, I've even purchased bows that did not quite fit but took it to my local shop for the correct draw length modules, paid the difference and still made out enough to get a rest or sight or other accessory and more. But do your homework before you bid to be sure the model you're looking at can be altered it not your fit.