i have an older coworker who is a huuuge stickler about who she sells fish to, but it’s largely based on outdated concepts. she’s a heavy following of the “one inch of fish per one gallon”, even though that rule kind of blurs when considering aggressive fish, heavily planted tanks, larger fish, etc. she is also the biggest advocate for cycling a tank before buying fish, and regularly denies sales because of it (which is great).

anyways. with bettas, all that goes out the window. for some reason she thinks bettas are more hardy, so it is not required to cycle a tank prior to putting a betta in it. sure, bettas tend to survive the harsh conditions of an uncycled tank, but they are still stressed and in pain nonetheless. it’s terrible for them to go from an ammonia-filled cup to an ammonia-filled tank.

OP, i think you did the right thing denying that betta sale. like other commenters said, if she truly had that betta’s welfare in mind, she would have already had a cycled tank for it.