This kind of thing gets lots of professors worked up, at least according to the Chronicle of Higher Education. Although I really don't like the idea that students sign up for a class solely to get off easily, or that someone is taking advantage of students by selling them this kind of information, I'm not bothered by rating services. I say so what? I expect a lot of work, and at the same time, I am happy to give students good grades who complete that work. I don't try to hide that. I believe all students have the potential to be "A" students, and should have the opportunity to resubmit work that is poor. I also believe "B" is a perfectly fine grade. Also, I take feedback and evaluations very seriously, and try to collect such data myself.