Would it be possible to add to the Pet Information to add a Trading Tab? How I'm thinking this would work as to not do a lot of spamming: On the Pet Collection page, there would be another option of view, like a list form. Only the Trade-able pets would be listed. You would have check boxes for Gold (maybe and option for how much gold) or Trade. When the box is checked on all the pets in question, you would be able to save your choices.
This information would then be moved to that tab for the pet.
So on the Darkmoon Rabbit card, when you access the tab there would be a list of names of the people willing to Trade/Sell their dmf rabbit. You could click on their name and it would Direct Message them to let them know you are interested. Also this could show a list of pets the person is willing to trade for. (Also something they could have under their profile.)