Welcome to the forum! I have two betta fish that I've rescued from Walmart and I've had one for over 6 months and he's doing great! Sadly one of them that I bought passed away, but my other two are doing great. I hate seeing them stuck in those little dirty bowls. Some of them have fin rot from the dirty water, so if you wanted a healthy betta that you wouldn't have to treat, I'd go with Petco or Petsmart but even they get bettas that have fin rot so it's up to you! :)
I have a question for you. You see im About to get a new Betta Fist and i'd like some advice from someone who has oned may betta fish in their time. ive had 3 before but they always got eaten my my cat (who i dont have anymore) so i thought id try again. SO my question to ask you was if i should get a betta from Wal*mart.