Here is what really happens to them: Last year, Jeffrey Nally was charged with 29 counts of animal cruelty because of the massive number of dead animals found on his property in the USA. Nally had obtained the animals through "free to a good home" ads.
Dog fighting circles use free dogs as 'bait dogs' to 'live train' fighting dogs. The animal you expected to be a pet is used to bait a fighting dog and is literally torn to pieces.
They get sold at flea markets or auctions to anybody who comes along. Most of the time these animals are neglected, kept in cramped, unsanitary conditions and often become sick and diseased.
Other sick people, called 'Bunchers' scour classifieds for free dogs, then sell them to laboratories for animal research and experimentation. At the research facility, the animal almost certainly suffers horrific abuse and most likely will be euthanised after the callous researchers are finished torturing it.
They get used for breeding stock in a 'Puppy Mill'. The living conditions in most of these establishments are deplorable. Bitches have continuous litters, one after the other until they get put down or abandoned when their bodies cannot force out another batch of 'money-makers'. Breeding does not just apply to dogs but also cats, birds, small mammals e.g. hamsters, mice, etc which are used as food for the exotic pet trade, and in many cases fed live and terrified to snakes and the like.
Animals are used in the security industry where they are kept in small, barren cages and trained with inhumane methods.
They are also exported out of the country for unknown reasons – transport is un roadworthy and many animals are transported in extreme heat or cold in closed goods trailers or hidden in boots of cars as export papers are not legal.
Cats are used as ratters and expected to fend for themselves. Even horses and other farm animals have suffered from free to good home adverts.
The people looking specifically for 'free to a good home' animals will go to great lengths to appear legitimately interested in providing a perfect, loving home. They present themselves as kind, responsible animal lovers. They often bring children along to meet the pet and owner to avoid suspicion. They will make up elaborate stories about previous pets, a perfect home and garden, and promise to provide a loving forever home to the helpless animal.