Even if they DO purchase them, it's honestly not enough to make money on, it more or less makes it cheaper to have your aquariums.
That all depends on how good you are at the business end. A friend of mine breeds angels, he is retired & has time to do more water changes, wheel & deal with brokers, drive distances to auctions & swaps, and hang out & push sales at shops. We have a gentleman's agreement about dealing with each other's customers.
This guy is good at the sales end, it's fun to watch him work. He brings in around $5,000 yearly, and puts around $2,000 of it back into running his 25 tanks. He figures with the time he puts into it he makes 3 or 4 bucks an hour. Still, it pays for a couple vacations a year for him & his wife.
I'm not retired, and would be far ahead if I spent the time I do with my fish working instead. It all depends on your individual situation. Many times moving what you have bred is tougher than breeding.
I'm surprised more youngsters with time on their hands don't breed & sell at auctions if they live near any decent size city. If you sell 50 bags at an average of $3 each, that's $150. Clubs will take around 30%, so you net around $100, tax free. Sell something a little more desirable, and the price for each bag goes up, as does what goes in your pocket.