I used the CarFax service about 3 weeks ago and it was the best $29.00 I have spent in a long time. It saved me from buying a dud from a dealership. Even though I told the salesman I didnt want a vehicle from a certain area or that had been in an accident, he didnt didnt say anything. So I CarFax'd the van and it in fact had both of the things I didnt want.
Think of it like insurance, nobody likes to pay for it until you need to use it.