I get offers like this all of the time. Probably more so because people know I am gay.
No, I would not do it. You're selling your body like a prostitute. Would you stand and flex in front of someone in person while they jack off? Because that's what they will be doing. Is this what you put all of your hard work in for to sell your body to a bunch of perverts to watch and jack off? Not me, I have more respect for myself than that.
If I get an offer to pose for Muscle Development or legitimate bodybuilding site, yes I would do it.
Muscle Asylum Project Athlete