Defeinitely not a rip off. As mentioned in other posts, basically you do a guided tour of the house reef. They make sure your skills are up to par. As an instructor, I've had to do this just like everyone else. It is pretty much a standard there. The house reefs there can be pretty good and will blow away a lot of other diving in local spots like the caribbean. We've stayed in sharks bay twice now and the house reef there is pretty good.