I've bought several used things from ebay, and they all came out fine. You need to read the sellers feedback, and read the entire item description, and also trust your instincts i guess. I just recently bought a firebox for the cheapest price i've ever seen, and at first i thought it was messed up, but turns out i just didn't install the driver correctly. So, you need to factor that in as well.
And for recommended sellers, people sell random stuff on ebay, the ebay stores that do have stuff always in stock are not much different than places like guitar center. So i guess i can't really recommend any.