At least try to find someone with a really high feedback rating. If something is amiss they might be more likely to try to solve it than just ignoring you after the fact. I would also ask the seller if they will guarantee it is in properly working order at the time you purchase it. That doesn't mean it won't fail the third time you use it, but it also helps you make a claim against the person for your money back if you have it in writing that they know it is working at the time they sell it to you, and then it is defective when you get it, etc...
