You can see some work that I've done, both in studio and on location, on this company's site.
Some of the animal shots are from my stock; any image with humans was taken in my studio or on location, with instructions from an AD.
"Models" are local veterinarians and their clients, a hired actor/model, and some ad company personnel that were drafted. Everyone except the ad company folk were paid for their work. All pets are purely amateurs.
The ad agency received the raw files and all rights to them, and were billed accordingly.