Ask for pictures of every possible angle, back, belly, growth rings (close ups), and make sure that the pics you recieve is the exact stave that your going to get. Ask lots of questions and if anything seems fishy, don't buy it.
Be sure to use paypal if your buying off of ebay so you have buyer's protection.
I have been selling staves for over a year now and most of my payments come in the form of money orders and haven't had a glitch as of yet, but I don't use ebay at all. Not trying to make a sale here or anything, just letting you know the experience I'm speaking from.
I would honestly look around on other trad archery websites and buy from sponsors on those sites before I trusted someone on ebay that may or may not even know anything about the wood they are selling. Just because they can drop it, split it, and list it doesn't mean they know all that much about it. Or try to make it to one of the many trad functions like MOJAM where you can hand pick your own and actually talk to the seller face to face would be the best case scenerio.
Food for thought. That's my 2 cents.