A person should not own a betta fish without knowing its gender? Isn't that a bit extreme? Does the same go for all fish? I still don't know the gender of my 10" inch pleco I had for years. Some fish's gender are just incredibly hard to tell. Even breeders with years of experience make mistakes sometimes.
Like, take this fish, for an example. Male or female at first glance?
She is a long finned female from Aquastar71. I mistook her for a male rosetail (which often have short fins than normal HM) at first, before someone pointed out that it said "FEMALE" in the auction listing. If she was a betta I found in a mislabeled cup at Petsmart instead on Aquabid, I would never have thought twice.