Nah, Bashir would devise a clever plan to everything work out just fine without people returning their carts.

Also, I'm pretty sure you got Garak wrong. He would promise never to return the cart, make a loud point about it for everybody, and insist on the subject every chance he gets. Just to covertly return it when nobody is looking because when Cardassia befriends the supermarket his people would benefit from the carts being correctly parked.