How much crueler can people be?

Ugh, that is despicable. Just like those poor glassfish that used to have dye injected as well. Check with the seller if they realize that it's a cruel practice in case they don't realize. If they continue to buy such fish, tell them you do not agree with their practices, and won't be buying anything else from them either, and will also be telling all your friends (don't curse, and stay calm). Write a letter to their corporate office as well, explaining your concerns.