I have rented on three different occasions and each time it went extremely well. Once for a crusie and twice to pay for an add-on. In each case I set up the payment schedule and gave a slight break in the price for those who were interested in paying 100% up front. I also searched the posts from each of the people I rented from to get to know them a little better. It's amazing how much you can learn about someone from their past posts on this board. We did everything by e-mail including setting up the "contracts" that we each abided by. The one thing about renting is that if you don't get the money, you simply can cancel the reservation. You are no worse off than before you rented unless you used borrowed points, which I would advise against.
IMHO the rentee is taking more of a risk than the renter because they are sending money to a complete stranger who still has control over the points.
Good luck.
HBC