I loved it! The art is incredibly well-done, everything looks amazing and blends in so well, but at the same time it never steps outside of Gameboy limitations, so it certainly could be a game made for Gameboy. Even all the menus and hints look amazing. I liked the store management part of it, with all the different characteristics and features of the fluffy ones, although for some reason at first I thought it was going to be more like Atelier but with magical pets, haha.
Like the commenters below I reached a point where none of pets I have could satisfy customers' demands, although I suspect you could present a pet they do not want a few times and make them go away, repeat until a customer with a demand you can satisfy appears. Some minimal SFX could be nice, at least some random Gameboy noise on confirmation or something like that, but a jam is a jam.
I actually liked this game a lot, are you planning to continue developing it? I could see it being a nice & cozy store management sim in the future, possibly for a small portable console like Miyoo or Playdate :)