Ebay is fine as long as you understand the rules of engagement, namely that there are fees involved and sellers can be unreliable.
Any sale of something you have previously bought will result in 14% going off to Paypal and Ebay combined. Therefore, if you want a reasonable guarantee on not losing money, only bid up to 86% of what you think you can sell it for, including postage. If you are a dab hand at taking photos, buyers will pay a small premium for well described stuff, which can mitigate the cost of fees. I actually have a little spreadsheet which tracks what I have bought and sold, and what I currently have in my collection. The net cost of Ebay including fees, if I would sell all my kit at a fair price would see me up by about GBP 500. Not that the time I have spent going to the post office has been compensated by GBP 500, but its a means of making sure I don't get carried away, in particular, the inventory aspect of this means that I can curb LBA.
Ebay is particularly great for building a collection of camera kit, I think. I have a nice enlarging lens from Ebay, a Fujinon EX 75mm f4, which I picked up for a fair price in comparison to other enlarging lenses. It would simply not be possible to buy this elsewhere (maybe other than on APUG). I have built a Bronica ETRSi kit up through Ebay, but only bought the body and lenses which looked like they were in good condition, and came with boxes. With unclear auctions, I just don't feel the risk of receiving something faulty is worth my time in terms of resolving potential problems. For my 35mm kit, it took a while to work out which stuff to buy and I have bought and sold a lot of stuff in building up my ideal collection (although that's still open to question). Once I had decided on Pentax, I have had stuff serviced, lenses and bodies, in order to get the best performance out of them. Its a little unrealistic to think 30 year old camera kit is going to perform at its best without some TLC.