Remember that places like eBay and CraigsList are only safe if the seller is safe. I'm not telling you do not shop there, because you can always find great deals, but if you ever have any questions about a product or seller, you can always ask here first. There's always a high possibility that someone has either owned said product, dealt with said person or to some extent heard about/researched the product you are inquiring about.
As others have said, AtomicMods, Xmods Internation and eBay are about as best as it gets.
Cheers,
Kyle.