Recently had one of my more interesting shops - at iFLY indoor skydiving. No payment, but the MSC provided a gift certificate code to make the reservation, so nothing out of pocket either. I know some people won't do any shop that doesn't pay you a fee, but this was a blast and it was $200+ I would have never spent of my own money to try. I got to bring a guest along, the package also included photo and video purchase, and the place is less than a 10 minute drive from my house. The report was pretty easy, and it required pictures but this is the kind of place where everyone is taking pictures and videos anyway so didn't even need to be sneaky about it.
Really fun experience that I wouldn't have had if not for getting involved in mystery shopping!