I trade fish all the time, just not back to an LFS. LOL
Honestly, when I get fish, I have a purpose for them...to enjoy.
I try to make sure that I have the room for all the fish I want, and if I don't....I don't take/buy/adopt the fish. I love every fish I see, so saying no is hard, but I try to think about the happiness of my fish and try to give them all ample room to grow and thrive. If I can't do that, I don't take them on.
I'll admit to breeding fish with the thought of getting rid of them. For example, I have convicts that I don't intend on keeping any more. I have a guy in town that, supposedly, wants them. I still have to check for this last batch. After that, I'll be finding someone who wants the parents, as I don't want them to breed any more. Right now, the pair is in a 10 gallon tank, awaiting some sort of conclusion from me. I do have an auction at the end of the month that they will be going to, if nothing else. As for the rest of my fish...I have them just to have them, even better if I get them to breed, as I'm hoping to do with my L15s and my BNs. Honestly, I've reached that point with my fish, where I'm getting breeding stock, with the thought of selling/adopting out the children as they grow. I'll have to see how that works as they breed.