Females are often striped when they are stressed, that's their stress colours. I'm currently trying to sell 7 of my baby Bettas but no-one is interested
. All the LFS around my place have said I'd be better off selling them privately because they'd only pay wholesale price for them which isn't much at all.
I'm not sure whether people don't want to buy them because they are babies or because there just aren't any interested people at the moment. Maybe I'll wait until they get a little bigger and try again. They went through a patch where they weren't growing at all but in the past 2 weeks they have really taken off and some that I previously thought were female have turned out to be male. I've put them all near my adult female and all the males intensified in colour and started making bubble nests hehe good way to sex them if you ask me.
I don't see anything wrong with buying baby ones, just means you get to see them grown into their fins and personalities as well as the fact that you will be able to keep them longer!
Good Luck if you do decide to get a new one.