Even buying legit items off Ebay can seem complex for some people with little web experience and no experience with the site itself. If you think about it, Ebay does have a fairly complicated process compared to other commerce sites. It's easy to discredit this theory when you've been online since 199x but I know a few folks, mostly bookish sorts, who'd fall for any of these scams in a heartbeat.
The mythos of Ebay as the sort of place where perfectly great items fall through the cracks and can be purchased for half (or less) of what they should cost seems to confuse the reflexes of some people who do possess tried-and-true common sense but fail to put the pieces together in time. And then of course there are just plain greedy people who don't/can't/won't learn their lesson without being burned to the 12th degree four times over.
I really blame Ebay for most of this at this point. Their security policies are limp-wristed at best and they are infamous for taking little to no action when deals go sour. Whether you use Paypal or not, customers are basically on their own in 9/10 situations and yet Ebay constantly market themselves as being nearly as safe as shopping at a store. They're not.
A flagging system similar to what is used on sites such as Craigslist would do wonders in terms of getting scam listings delisted very quickly by the community. Such a system would require a certain number of flags to be raised by a certain number of unique users to raise the level of danger associated with a listing and eventually delist it automatically once a certain threshold is reached. This would keep competing sellers from fraudulently attempting to delist legitimate competing items while simultaneously getting scam listings out of the system much faster than it currently takes Ebay customer care to individually review and delist things. Making it easier for users to get involved in policing is key (the current system requires you to actually send a message to Ebay customer support to report a scam after going through two other steps and dealing with all sorts of pull-down menus, etc. A flagging system would be a one-click method of participating.)