When you went to get the snake, was it already out of the cage when you got there? A snake doesn't go docile to hostile in 5 days unless something is really wrong. If you didn't see the original owner take it out of the cage, then it's probably just talking a big game to get you to leave him alone. I'm sure when he's out, he'll be just as nice as when you first saw him.

My RTB hisses when she's in shed, could that be a possibility? Is RTB in the 160 gallon tank you have or did it come with a cage? Explain the setup.