Well there's not exactly any sort of screening process for being allowed to advertise on CL, and it's probably the cheapest way for SPs to advertise that still gets results. When you combine those factors, that means that a very high percentage of the bad providers out there (and by bad I mean scammers, wastes of time, bait & switches, etc) will advertise on CL. That doesn't mean that you shouldn't use CL (although I have to admit that I don't), it just means that if you see an ad that you like the look of, you should do a little research first. There are plenty of reputable SPs who advertise on CL, but there are also plenty of disreputable ones who do the same.