The thing is, they are a franchise, different organizational structure than a chain. A chain has a store manager, who answers to a district manager, who answers to corporate. The store manager, district manager, none of them have had to invest any money in the location to get it or keep it running.
A franchise has an owner, when all is said & done they have invested around $230,000 to get their Petland store open. They have much more say about how the individual shop is run, and you have a better chance of making any headway with a situation such as this. They also reap the profits or eat the losses of their shop, very similar to an independent shop.
They have invested quite a sum of money to get the nation wide exposure, while having the freedom to work their shop as an independent. If you expect to accomplish anything you have to remain as emotionless as they are about their product, while hammering home the money aspect. Carry yourself as a businessman when dealing with a business owner and you will go much further in achieving your goal. Act like a reactionary petition signer, and you will get blown off, they are good at what they do, as they do it for a living, and have the backing of the franchise as far as how to handle the situation of a disgruntled customer.
Schedule a sit down meeting with the owner. Have solid facts on the breeding of bettas, as well as the care required, ready to present. Explain that you like their shop, want to see them make a profit, and don't want to see any risk of them going out of business, being your favorite shop. Afterward, write down the conversation, what was discussed & covered as well as decided, as soon as possible. This documentation may be of use in the future, should they decide to go back on what was discussed.
Most people deal with shops from the consumer end, I deal with them most often from the supplier end. This gives you a totally different perspective, puts you on more equal ground with the owner, with access to information not available to the retail customer. You can take what I'm telling you & use it, or toss it, I'm just trying to point you in the most effective direction.