Is it legal? In one way or another, most likely not. Even if you assume that all it is some ordinary, innocent home butcher, which it probably is not.
Every place has regulations about how large animals are disposed of - and how they have to be handled, fed and transported beforehand, and even, how the carcass is handled/cuts are refrigerated, etc. Most states require any animals intended for human consumption must be inspected and certified by a trained inspector, safe for eating - in most cases a home butcher is very limited even as to what he can do with the animals on his own property, let alone letting them go somewhere.
There are a lot of backyard slaughter yards these days. They are illegal in most states in the USA. I think that's what this one sounds like.
That he does not take horses is odd, but most likely, he doesn't have much call for horse meat.
This guy is probably running one of those illegal slaughter yards.
A lot of animals are getting stolen these days, and people will get a couple dollars for them from a guy like this.
They keep the animals in very bad conditions, don't feed them, til they get a call for that type of meat, then the animal is put down - usually very inhumanely. It's pretty nasty. They try to stay below the radar so they can run a filthy place and not take care of the animals properly - that costs too much. There have been a couple exposes recently about these places in my area. A lot of them are within the city - the animals are in tiny pens with no shelter.
There's something odd about the ad though, that makes me think he's not running an illegal slaughter operation or feeding a pack of hunting dogs, as he emphasizes that the animals are being 'bad'.
The other possibility that occurs to me, is that he is one of these 'snuff guys' - they video tape torturing and killing animals and sell the videos on the internet to - to people who are interested in that kind of thing.