I am so sorry for your loss! SIP at the Rainbow Bridge.
IMO, baby bettas are challenging. They have require warmer water, smaller food, etc. Some people on this forum have had great success with babies, but personally, I prefer the adults since I know exactly what I'm getting.
The chains vary in terms of their care. If the store specializes in pets (Petco, Petsmart, etc), then speaking to the store manager can help. These stores want to maintain a good reputation with regards to pets. If the store doesn't specialize in pets, speaking with the store manager may, or may not, be helpful. It just depends on the store.
As for rescuing fish, if they have an illness, sometimes they survive, sometimes they don't. It just depends on the disease/condition & how far it's progressed. If you want to rescue one, look for one that appears active AND healthy, but whose cup looks icky. Most of the time, all they need to recover is some clean, warm water & good nutrition
I wanted to say thanks again for your help with trying to get my fish better. I thought it was over and was ready to get his tank prepared for his return from the bowl only to wake up this morning and he did not make it. :( My husband wanted to buy me a baby betta he saw at the pet store this afternoon. I have never raised a baby fish so I told him not to get it. I was wondering what your thoughts are on this. Also I have a problem with going in those big chains and seeing all the sick fish, it makes me want to buy them all and save them.