Ok here's an idea. Say I have a pet that's bought and great for me, but I don't prefer the skin of my pet 
I recommend adding the in app feature of changing the pets skins to another skin inside the monsters class I.e mage pet gets New mage skin. Melee pets get melee choice of skins. If archer pets then the selection of archers skins... And so on. I know a lot of players who would pay a few bucks to get rid of their ugly worms skin. Tell me this isn't a terrific idea