This is a tough one (for me at least). On one hand, it is dishonest and under-handed. However, it is (still at least) a free market system we have, as well as a buyer beward environment. While, I wouldnt personally get an injured or sick or unwanted animal and advertise/sell it as something its not for a major profit, its not illegal (depending on if they are licensed to operate as a non-profit organization). I get sick animals in quite frequently in my animal clinic and I choose to take many home and rehab and nurse them and then adopt them out for either a small fee (to ensure a good home, not usually more than 40 or 50 bucks) or I let them go to an adoption agency type place (dependent on the type of animal). But, its not illegal (unless otherwise implemented by the seller that they are non-profit), to get a free couch, for instance, fix it up and then sell it. Animals, are unfortunately, considered propery, legally, so law wise, its no different than fixing up a couch you find and selling it. Morally, ethically it is wrong and just deviant, but not wrong in the eyes of the law.
All you (and any of us) can do, is expose them and hope that some poor young and/or inexperienced person doesnt get taken. Reality is, it happens everyday, with many many many situations.