IMO, it just depends on the purpose of the betta in a vase. If the person thinks the betta is going to eat plant roots or fungus on the roots, then I think they need to be tied up in a dark room for a long long time.
If they just have a betta, in a vase, and FEED it and CHANGE the water, then, ok...I can live with that, because it is a pretty set up if maintained properly.
Here is what I think is beyond stupid. I saw this today on aquabid. A person is selling a betta, in a vase. Thats all fine and dandy. BUT they are selling it with a floating candle in it. LIT with Mr. Betta in there. Now, I know the betta isnt going to attack the candle (well....it could happen) but we all know bettas will jump. And my very well land right on that lit candle. I dont see this as a good idea.
Ok....Im off my soap box now
Amy