Check their ratings on eBay. Just don't forget that these buyers have the profit motive. They will never pay you what some guidebook says your card is worth.
Often wondering, myself, if I am getting a fair shake selling my "vintage trading card" collection, my advice is attend a few major regional card show and network, network, network!!!
Call your insurance company for a basball card appraiser reference. Check online for a general idea. Don't give information online. Go to a baseball card show and "ask around".
Well if you are talking about dealers, then you should go straight up to ebay and check what the local bidding rates are. Because of that you can assess whether your getting a deal.
