I have never sold anything out of my tank but I will give it away. I don't know anyone near here with a tank so I may give it all the the Public Aquarium near here.
We may take a fairly long vacation this winter and If we do, my tank may crash. A tank sitter will just feed them but knows nothing about problems or if it runs out of water.
If that happens, there won't be anything to give away except a smelly bunch of water.
The last time I went away for a week my tank sitter let the water level fall about 7" and didn't notice.
I lost all my big acropora and many other corals, but the fish seemed to enjoy the added salinity.