Okay, I agree that when the store purchaces a fish, any fish, that they should be able to sell it for a reasonable price and make a fair profit.
If the store paid the same for this pleco as all the commons, then you could not be ripping them off, they are still getting a fair profit. If they paid more for it then you are 'ripping' them off in a way, but who knows for sure?
I agree that if they had a price on it, that was fair, then I would also buy it at that price. The issue is they had it in a sale tank & later said 'not for sale'..
Most of the LSFs here have display tanks marked 'not for sale' as well a 'Q' tanks for new fish. If this was in a tank will sellable fish then it should not be quarantined, and if it is quarantined then is should not be in a sellable tank.
Of course, that is just my opinion. I have been wrong b4...