eBay offers a great range of cymbals for sale. You will always find great examples of the top five ie Paiste, Zildjian, Sabian, Ufip and Meinl. Turkish cymbals are now also readily available like Bosphorus and Agop/Mehmet Istanbul etc. Some of the best value can be found buying classic versions of old Paiste and Zildjian cymbals which are no longer available retail.
Before deciding to bid, DO YOUR HOMEWORK. What sort of cymbal do you want? What sort of sound and what styles of music do you play? Go to music stores and check out the cymbals they have. Play them and get a feel for what you want. There's good stuff and there's also some rubbish. Just like drums, they won't run out of cymbals on eBay, so wait until you see one you know you REALLY want, then you can bid with a better chance of getting a cymbal you'll be happy with.
Once you know what you like/want, you have a better chance of getting the right cymbal. It helps to go to the Manufacturers website and listen to their sound files, so you get a bit of an idea as to how a cymbal will sound. But a cymbal will always sound different once you play it with the rest of your kit, at the volume you play and combined with your other cymbals. It is much better if you have heard the cymbal you want previously, and know what it sounds like.
Good luck, read the page carefully, check feedback, check payment methods, check postage, ask questions and......