The Fish and Sam, during the Fish Tank reveal they said it was in their contract and some(but embarrassing for them, a small few) of the Fish had read it. IIRC Mizzy was one of the ones that read it and knew that was in their contract.
The first gas light was that the Grand Prize was only $5k. I figured out pretty early when they were asking a lot of the Fish if they read the contract, that I'm pretty sure that was a check. The contract probably gave more of the show away then they wanted, iirc Mizzy also knew there was some mentions in the contract that lead her to realize the show was live. The first week they were definitely trying to sus out who had read it, and I think saying the Grand Prize was only $5k was ito get people to speak out.