If you don't think that you are comfortable with it, then I would say don't take it. If you are in a position to, maybe go see it in person a few times and see just how aggressive it is. Possibly, if it has been used as a breeder, it hasn't been handled much and might calm down with regular handling. I'm not sure what size of tub he is being kept in, but a 5ft boa should be in something like a 4 X 2 enclosure, or a VE-175 tub, and would probably appreciate some type of branch, poles, or shelf to perch on. If you decide to get him, definitely get a hook, if you don't already have one. I have all of my snakes hook trained so they will be used to it once they reach adult size. Good luck with whatever decision you make.