Because they are same specie as horses?? just they are live in the wild...
Only REAL wild horses are Tarpan (Europe) and Przewalski's Horse...Asia... You dont have true wild horses in America
Quote from wiki : The term "wild horse" is also used colloquially to refer to free roaming herds of feral horses such as the Mustang in the United States, the Brumby in Australia, and many others. These feral horses are untamed members of the domestic horse subspecies (Equus ferus caballus), and should not be confused with the two truly "wild" horse subspecies.
Yes theoretically You need a license to sell You Hamster your guinea pig parakeets beta fish to another person...
As wolfy said cats and dogs are "domesticated" animals and they are put in to different shelf but for SELLING anything what is not domesticated You need to have Proper LICENSE...
Why Do you Thing Craigslist have disclaimer that is NO ANIMAL SALES but adoptions ??