I know of a couple of bird flippers in my area. Yep, they will contact the seller, whether it be on Craigslist or Ebay classifieds or where ever and offer them a lower than asking price for their birds. They usually go for the desocialized birds and the ones with issues of aggression, plucking, and so forth.
But what I have found about the couple that I'm familiar with is that they actually do a great service to the birds and the buyer as well as the seller that they bought the bird from. Here's why I feel this way
1. The seller is selling a desocialized bird with biting or other issues, which keeps the seller from selling the bird to an inexperienced bird person. The seller gets to unload their unwanted bird and make some money while doing it.
2. The flipper, then works with the bird sometimes for months to resocialize them and actually turning them into a pet again.
3. Then the flipper finds the birds a new hope and yes, at a higher price because they have re-tamed the bird again.
4. But both flippers here will not just rehome te birds with just anyone, they will deliver the birds to the buyer and do a home inspection in the process. They even do a couple of checkups on the buyer and the bird to make sure everything is going good.
The couple I'm familiar with, I wouldn't hesitate to buy a bird from them because I know how they care about the birds. Is it a business to them? I would say NO, it's more of a hobby. But I'm sure not all are this nice or good.