A good way of making some devs getting some more money from players without any shady tactics would be to have all pets function to pick up Shards & Glyphs.
If pets were to cost lets say
5 $ ( for pets with default skin )
8 $ ( for pets with special/shining skin or some kind of aura around them )
12 $ ( for all 3 above & special limited time/unique pets )
I think this would be fair play, and it would not make game feel pay2win or anything like that.
Selling such advantage as item pick up should not be an issue.