I really wouldn't stress about that, thekath, a lot of us (myself included) pity purchase sick fish, and they're from stores with bad care policies. I brought home 6 sickly walmart bettas last month. As long as there's a mass of uninformed (or people who just don't care) buying them, there's not much we can do outside of educate and/or boycott. And while boycotting would make a bigger impact, people like me can't sit there and just let them die.
It sounds like he's off to a good start with you, hopefully you can get him patched up. And great thinking on the hammock, it'll make things easier on him in the long run. ^_^