done it twice. really good way to save money but it is riskey - the DVC owner can cancel a reservation at any time . And although it seems rare on these boards, I have heard of at least one negative experience in the past.
I suggest that you do not post a "want to rent" message. Just wait and watch and when someone posts a "points for rent" message- then you can get an idea about who that person is by reading past posts by them etc... I would only rent from people who have a long post history (not just 1 -3 posts) and who are very open with information. Ask for references.
The last time that I rented, I drew up a short agreement/contract - we both agreed to it's contents by email and then both signed and made copies before any reservation was made or money exchanged. This way, both of us at least have a piece of paper spelling out the agreement.
Once you rent the points, you have that reservation and although some folks will make a change for you if necessary (or if they are able to) - mostly what's done is done - so be sure you want those dates and intend to travel because generally it's a no refund deal. There are more restrictions with using points - so make sure you understand that before renting.
good luck.