Well, to clarify I wouldn't spend $15.99 for a sick betta, but most bettas I see are $3.99, so to me that's not too bad. I guess I should clarify and say not necessarily "SICK" (like swimbladder, dropsy, ich, etc.), but just the ones that look sad, drab, and thin compared to the "new arrivals" who would be spotted and taken home soon.
I don't know. I guess I'll "know" the right one when going to pick one out, but I can't help but be drawn to the less fancy ones who would probably become beautiful with some TLC. :)