Something that I do, even if it may not be the right thing, is rescue bettas so that none of them die alone in the back of a shelf or being shaken until their eyes fall off and they start bleeding like the poor fish on this thread :'( Even if you don't have the money to buy all of the bettas, if one of them that you bought dies, you can return the same body again and again for more betta fish, for free. :) You could keep the body in a freezer, and I doubt anyone at walmart knows enough about bettas to think it is a different fish.
Evalin-Royal blue and red CT
Myah-Red cambodian VT with red head
Estella- Royal blue CT
Zippy-Red/white/purple dragon PK