The other day when I was at petco to pick up a heater, I ran into a lady trying to buy a crowntail betta for her 12 year old. I guess her kid asked for one. She'd grabbed a sickly crowntail, and I sort of corrected her-- it was moving but all at the bottom of the cup.
She was headed for one of those small betta 'tanks' that I swear are the size of a soda can. But I told her that her fish would be a lot better off in at least a 2.5 gallon tank, and with a heater for it. She grabbed a decent little home for him, and seemed happy for my help. But it makes me mad that petco sells little tanks hardly the size of the betta cups right next to them. :/