Never heard of them but somehow I suspect that for "only" $29.99 or something similar tbut you they will sell you a list of companies you can sign up with.
BTW, rather than spend money for such a list your are welcome to use the free one here in the first post of the first thread of the Mystery Shopping Company Discussion section of the forum. You can't beat the price and they are legit. There are a couple of them that I think now may be charging a fee but frankly you never should pay a penny to shop. The purpose of this endeavor is for companies to pay YOU to do their work.