Several questions -
1 - I wonder if this would affect your personal insurance. Renting your car would likely affect your insurance rates or possible even void your policy.
2 - The government allows a deduction of about $.55/mile for driving your car for business purposes, but these people pay only $.10/mile?
3 - And what if something does happen to your car?
4 - The math - for all of the risks involved, you save about $15/day parking and make possibly an$2/day. I think someone would have to be in pretty tough shape to take such risks for such a small return.