I think it would be a good idea to add a rating system for rigs as well.

After 6 hours of mining (at least thats what I would use) the renter is allowed to rate the rig 1-5 stars and put in a comment about the rig.  The rig owner should also be able to make a response on the feedback given by the renter.  I would also like the list of rigs to be sortable by Hashrate, Price Per Hashrate, and Rating for the rig.