I got a baby Betta from my Petco. As far as their store care goes... it depends on who is working there that week/day I guess.
The one I picked up was "tadpole" size when I got him. I have to say I've thoroughly enjoyed watching him develop.... However like Aus said, the vast majority of people who buy them probably won't be on this forum, or any
forum for fish most likely and they won't know they need more care and extra needs. I'd say people who have been studying and researching how to breed bettas and care for the fry would be most prepared to successfully raise the babies to adults with no issues.
So overall I'm against them selling them without FULLY informing people but for those who don't wish to breed their fish but want to have the experience of raising a baby it's a good learning experience. (My baby is a veiltail boy)
I do wish they would place their cups in a tub of heated water on the shelf at the very least. I don't think this would be too much to ask for. Zero out a heater for store use and get a storage box to put the cups in? Maybe provide some paper towels to wipe the cups at the station before you buy them. Or maybe make the store 90-100 degrees so the cups will all stay around 80 :D... but I don't think the shoppers or the employees would love me for that suggestion LOL!!!