Culls shouldn't be sold.
When fish breed, inevitably you will end up with culls. Not all "culls" need to be euthanized, but certainly not sold. You can keep them yourself in a designated pet only tank where their genetics aren't allowed to enter the hobby to affect the quality of fish we end up with.
I've bred a lot of fish, and I've had culls. If it's something that won't affect the quality of life, I'll keep as a pet only and allow them to live out whatever lifespan they have. Sometimes there's issues that are not good and it's kinder to euthanize them humanely.
Weird fins, missing an eye or so, eh they can live a normal life as pets, but terrible to allow those to breed further.
Some of my culls lol
hoplosternum punctatum, didnt develop pupils, 3 of these were totally blind. But they get on very well. But absolutely never will leave my care and are not bred.
this osteogaster had 2 tains and 2 adipose fins (the other was upside down)
Brochis splendens, born missing one eye, has half a ventral fin, and a bent dorsal fin. He trucks on very well with his normal brothers and sisters, and lives as a pet with the rest lol
But, it's really, really poor to distribute culls. It's unethical to do so