I've been buying off of eBay for years, and haven't been been burned in any serious way. Yet.
But I also don't bid on anything about which I am ignorant.
To avoid being eBay roadkill you need to do your homework, know what you are buying, know what market prices are, correspond with the seller, ask questions, ask for more and/or better documentation. If something feels too good to be true, believe that feeling and run away like the hounds of hell are pursuing you. People victimize themselves by thinking they are "smarter" than they actually are.
This in no way excuses eBay's predators, and if you are aware of one, report it to eBay. You have nothing to lose. Just bear in mind that eBay is a vast worldwide enterprise with millions upon millions of transactions happening daily. There's no way that they can police all of that and they're not going to try.