We rented points at SSR in 2008 and got an amazing deal. The owner was a family member of my son's business partner, so not a stranger, so even though I had never met them before, we didn't have a trust issue in any way.
We had a wonderful trip, but there were very minor negatives involved in renting which had more to do with me being used to being in complete control over my vacations and having to give up part of that control.
The possibility of cancellation worried me. Not only would we lose money, I had the extra burden of worrying what the DVC member might lose in the process as well.
When making ME reservations, you need to go through the DVC member because they are the only ones that can make those reservations. So if you needed to change your flight, thus change your ME time, you would need to contact the DVC member and they would need to call Disney to make the changes. I felt like I would be a pain in the neck if I had to make changes, lol. It felt odd to have someone else handle all that. And again, that is because of my vacation control issues... I want the ultimate power and all that, lol.
I actually like not having maid service, so that was a plus.
That is all I can think of right now.