This won’t work everytime, but for those times it does, this is a rather unique way to advertising companion pets for sale. It will get you quite a bit of head turning, and even some pissed off people when they realize you are selling the companion they so desperately want.
All you do, is rename the companion pet to For Sale, and then place your pet in an easy to see place near the AH. People will pass by, see the pet for sale, and then contact you, if they want to buy. If they do, then put it in a cage and trade to them.