Rescuing to at least means that you are saving a life but you are not encouraging the business to sell more at the same time. Really at least talk to the manager and say, "hey you have a sick betta, I doubt people will buy him in the condition he is in, can I take him off your hands" don't mention money at all, if you say you will take him for free or for a small price they will take the money. If they reject offer them a small price. Most managers are nice and will allow it. Buying a sick fish for full price is silly, like buying an Xbox but it is broken but you can fix it and you pay full price...
I just don't think paying full price is helping the animals in general, it helps the one, but not all. Just remember that... I think what you are doing is good though glad you do it, just remember that if they make a profit they don't care what happens, at least at a business stand point.
I totally get where everyone is coming from. The only thing is, while we are refusing to buy the fish, they suffer and die. And will continue to suffer and die because people won't stop buying fish, or any other pet. The choice is a hard one, and I agree paying the people who mistreat the animals will only encourage what they're doing. But the alternative is not great either, just letting the animals either die of illness at the store or going to a home with people who consider it a decoration, or "just a fish". It's an almost impossible choice.
Think, you can't save them all, so yeah, hate to say but they will always keep dying. It is sad and it sucks to hear it and know it but that is reality. Ask for the free betta or ask for a discount. Write complaint letters to the store's HQ. It is like the drug war for every bust there are many sales, bettas they save one and even more die...
When you buy fish in poor conditions you are simply making a spot for a new one to fill. Thus the cycle of abuse continues even though you spared that one life. Supply and demand - Stop the demand and they will end the supply. Stores do not sell things that don't bring in some kind of profit. It has happened in Walmart's across the country. Some have stopped selling Bettas and fish altogether.
We are only human though... Sometimes all we can see is the suffering creature in front of us, instead of the bigger picture. When I complain to managers, I usually try to convince them to let me save one Betta at no charge. If they refuse then I (with an extremely heavy heart) put the fish back and refuse to shop there anymore.
Sorry for that last comment. I just get my feelings hurt easily (wimpy, I know) and just wanted to do something good. I totally understand what everyone has to say, I really do. I thought I had figured out what I wanted to do with myself, so it was a major disappointment. Sorry if my comment seemed petty or rude.
It doesn't mean that starting a betta rescue isn't still a great idea. :) Just make sure you aren't paying money for the bettas that you save (for instance, advertise on Craigslist that you will take bettas people don't want anymore). :) That way, you aren't supporting any businesses that keep bettas in those conditions in the first place.
How about instead of buying post ads on craigslist that you will take in unwanted betta? ;)
Repeatedly buying may fuel the flame.. but as has been said before the real money is in all the equipment. So second hand equipment, or from places that have nicely kept fish. :D