My advice is to always do a search on several adult boards and google before signing up to a new sponsor. And keep track. Some forums have separate boards to report cheaters or scammers. Many even (like this one) allow you to subscribe to the forum as an RSS feed. It's a great way to keep track of bad sponsors!
I also keep a personal blacklist. When I see BS from a sponsor I like to put them on the list along with a few words in summary and a link to the post that made me place them on my blacklist. My list of bad sponsors is huge but ranges from horrible conversions to outright fraud on affiliates.
But I will tell you two sponsors that I highly recommend as being excellent choices for affiliates: Naughty America
http://stats.naughtyamerica.com/ and Kinky Dollars
https://aff.kinkydollars.com/ (note: no ref codes). I'm sure there are many more as well.
