Well, I'd say trades are enough. Even if setting up multiple trades can be a little annoying, at least you can't receive random Creatu you don't want from random people without consent. I imagine there are some out there who'd do that. And maybe even, in the cases of beggars who normally just send silly trade offers, someone would repeatedly send almost worthless Creatu in attempt to butter you up, then ask for the pet they want.
Maybe I'm just being paranoid with all this or something, but I think I'd rather keep the requirement of consent from both users. x3 At least with trades I can decline offers.
*has become neutral* o3o