Do NOT buy the ones that have genetic deformities or have any issues.
I looked about 14 different ones on Friday & I could clearly tell which tail types they are. Veils & crowns in my store.
Only 2 of the feistier fry caught my attention, but after I thought about it. I already have fry from my own spawn. Mine are clearly healthier, smaller & cute so I left.
One thing you could do is bring a little food from HOME & drop it in the cup to see if they'll eat it.
Nothing worse than a picky eating betta.
I've never fed mine BBS, but they've eaten mosquito larvae I had frozen from this past summer. Literally took them over 1 month since they hatched before they started to realize I was offering them food. Before they started to pick at the food I provided, the snails cleaned up all the bits of food they REFUSED to eat.
- StarZ pretty much covered it. Filter & heat are key points. Wrap the intake of the filter really well.
You've been a member of this forum longer than me, so you should be able to tell the subtle differences in the bettas.