Paypal's protection doesn't cover timeshare rentals, so don't count on that.
There's nothing particular about eBay that makes it riskier, but I think you have to educate yourself very thoroughly on
DVC and the point rental process before sending anyone any money. For instance, you don't want to pay for a reservation that was made with an RCI trade into DVC. That's against RCI's terms of service, and when they find out about them, they cancel them. You may or may not be informed by the seller that the reservation is gone.
The owner ALWAYS retains control of the reservation, no matter who you rent from, so yes, there's always a possibility that they can cancel the reservation out from under you. That's the tradeoff for the savings - a somewhat increased level of risk.
I would start with reading the "How to Use This Board" sticky thread at the top of the DISboards Rent/Trade forum, and the threads linked in the first post of that thread. They'll give you a good overview of how renting points works, and things you should watch out for.
While you're there, you can take a look at the point rentals that are on offer on that board.
Personally, if it were me, and it was my first time renting points, I'd use a service like DVC By Request, that specializes in
DVC rentals. You won't be getting bargain-basement prices like you might see on eBay, but you will have a reputable, experienced company managing the process for you. You won't be getting RCI exchange reservations. And there's some protection of your investment, since they withhold half of the payment to the owner until your arrival date.
Good luck!
