I think that if you're low on funds and you can't pass a fish without bringing it home, you might have issues. Those issues probably bleed into other areas of life, like buying things you know you can't afford because it makes you feel good in that moment. I have a lot of experience with impulse control problems so I know of what I speak. :)
I think that if you can't give an animal a good quality of life, then don't bring them home. If you can't give them a heater (and you live in a non tropical climate), don't bring them home. If you have no intention of doing the needed water changes on whatever size tank you bought, don't bring them home. If you can't afford to get them whatever meds they may need, don't bring them home. If you can't keep up with the water changes you have to do now, don't bring them home. And finally, if you find yourself constantly dividing tanks into smaller and smaller spaces just to bring home a new color you couldn't resist, don't bring them home. They're not collectibles. They're living things. :)
I wouldn't purchase a Betta from any source that was showing signs of extreme illness or distress. I'd rather not have to QT a fish in a tiny tank just to have him in my home if I don't have to. I've seen some people post about purchasing BECAUSE the fish didn't have a chance, and although I always feel bad for them and it makes me quite sad, I still wouldn't bring a sickly fish home if I could avoid it.
I make a point to tell the person in charge of that section if there are any dead fishies or if the water is so cloudy you can't see the fish to begin with and then I pick the healthiest looking one to bring home.
This goes for any fish, not just bettas.
I'm not a fish resucer, I'm a fish keeper...fish lover..
I guess my idea of "rescuing" would be what RiverStoneBetta did: taking a betta that is already owned and giving it a better life. That goes for all animals, not just fish. If I buy one from a chain store, it's purchasing/adopting, not rescuing. I have 3 VTs right now, and I so badly want to go into PetCo and get an HM, but I know that I don't have the time to have a smaller tank to take care of. So I just avoid the betta section. I know better, I like my 3 boys and my divided tank and I am happy. One day, if one of my boys passes away, that's when I'll get another.
That's what I consider a true rescue. Now that I'm mulling it over, maybe one of the reasons that chain stores don't do much to change the conditions of their bettas is because of fanatics like us that feel the urge to "save" every sad betta we see. It's diabolical, possibly paranoia, but I think it might be a factor.
I like what CJ, the owner of my previous LFS, said: "I only want people who know what their doing, or want to know, to buy my fish. That way, they'll come back here for supplies for that same fish year after year after year. Regular customers give ms the most revenue.
It's possible paranoid, RiverStone, but for a legit reason. I mean, I would hope stores wouldn't put their stock in harm's way just so us fanatics would buy more fish, but who knows. I stopped trying to figure people out a LONG time ago, haha.
We talked about some of these things in my thread about animal hoarding. I think it's obsessive compulsive behavior. We need to know what our limits are before buying more. I rescued 2 bettas since I've been in the hobby. One belonged to a neighbor who didn't give a crap about her fish and the other one was given to me by a cousin who was going to flush him.
I still have the urge to make bettas' lives better, but I know I can't buy them all, so the compulsion has died down for me a bit. And as I said before, now that I'm in business with an awesome LFS, I don't have to worry about leaving bettas in the store anymore. I have no compulsion anymore, and thoroughly plan it out. That's why I feel paranoid about large chain shops. They want you to buy a pet because it's cheap and there in front of you. Good LFS want you to buy a fish because it's healthy, better quality, and you get better information so you can keep coming back.