I'm about 99% confident that there is at least one older, lengthy thread on this opportunity, with lots of stories, including mine. As a buyer, working through these programs probably costs you nothing except possibly for realtor selection, as the commission is paid by the seller and the cost for the miles cuts into the commission the realtor receives.

As a seller though, where you have some negotiating power for commission, if you work through one of these programs, you are probably stuck with standard full commission. My experience a few years ago when selling my townhouse was that the realtor would rather cut the commission rate than work through a miles program, though I don't think one is supposed to contact a realtor directly first.