Why buy DSLR on ebay? Because you, like me, probably can't afford the latest, greatest, gear at high prices. But other people can and they upgrade regularly and then sell the old stuff on ebay to recoup part...
Scam Buyers, what to do! I'm afraid it does happen, you sell something and the buyer claims it is not as described, was never received or is broken. The most important piece of advice is ONLY to use ebay...