That's hard to say. A lot of my muses already have pets and none of them were picked off the street.

I might have to go with Red though, a scenario that comes up is an AU version of him where he attended a petstuck fighting ring and bought their bait troll off them so he could save her from getting chewed to pieces, and then he actually just kept her. It was an impulse save, and while money exchanged hands, it was definitely an accidental rescue adoption.