I am an owner and have rented a few times in the past when we weren't using all or any of our points.
For me it really depends on how far out you are renting, how much the total charge is, etc.
For instance, if I was booking 11 months out at my home resort (say for Xmas week) and I needed to borrow a certain amount of points to do it, then I would require an up-front deposit equal to the number of points I needed to borrow.
For instance, say it was 240 points, but I had to borrow 40 of them at reservation time, and I was charging $10/pt, then I would require $400 upfront and it would be NON-REFUNDABLE if they canceled the trip.
I don't think the owner should have to move stuff around point wise and then be forced to use it or lose it.
That being said, I also have a very detailed contract that I type up that protects BOTH parties, owner and renter. I am completely anal-retentive though and also make both parties have it notarized as well, so if it ever went to court, then it would be fully enforceable.
I highly recommend anyone who rents out or rents points sign a formal contract. If either party doesn't feel comfortable signing a document like that, then they should move on to someone else. I've had many renters tell me that they felt very comfortable with me renting to them because of that contract because I also deal with their fears/concerns as well. I think any owner that isn't willing to acknowledge the renter's precarious position in handing over dough while we can cancel their reservation on them is not an owner I would consider renting from.
Jenny