The only real concern for me here is the quality of care this guy provides for these "rescue" fish before he sells them on. If the care is good I have absolutely no problem with what this guy's doing. Even big rich let's rescue fish go to joe public now and again, though i'm not sure if he receives any monetary gain or not.
Like rich, he's doing a bit of a service to hobbyists who can no longer care for a fish for whatever reason and the LFS aren't interested in taking them back in.
If he cares for them properly, and like I said that is my only concern, then good luck to him. He's spending money on food and housing for the fish so it's only right he recoups some money somehow to help him carry on.
However, that said, if he isn't caring for these fish properly then i'd happily jump to the other side of the argument.
And as a footnote, you could flip this one right round. Why is this guy receiving fish in the first place? Because of hobbyists who haven't done their research in the first place when buying fish, and months down the line end up with a leviathan they can no longer take care of and want shut of it. Nothing new there, ask big rich! It's a bit of the pot calling the kettle black really. This guy is being called out for helping to clean up some of our fellow hobbyists mess.