Use good sense in checking the ratings. A few negatives don't mean the seller is a crook. Look at what the total percentage is, and what the negatives actually say. Some people use the threat of negative feedback to try and extort from the seller after they've won a bid, and some people will complain about anything at all. Whether you're buying antiques, ephemera, gems, jewelry or GI Joe dolls, your best protection is knowing the market.
Most sellers are on the up and up, and online auctions can be a great source of good buys.
Be careful, but don't be paranoid. Every eBay user is covered, at no additional cost, by the eBay Fraud Protection Program. This will remove you from the ScamBusters list. If you click reply, you will be removed from this list. It may take awhile for us to respond - we do this as a public service.