The problem with purchasing a tiny fish with the intent that you get rid of it is twofold.
First, who do you get rid of it to.
Second, if you are talking tangs here who could possibly get rid on one of these fish. You simply get too attached to them. I think there would be a tendancy to keep them longer than you should to the detriment of the tang and the other fish in the tank.
Example
Who would take Emilys clown tang. I would think that it would be too aggressive and too large for most tanks.
Having said that I would love to be one of the very very few who could keep a clown tang alive.
