seriously what age are you 12?
I can understand not wanting to leave a dog outside. Any old scrote could just come along and take it.

Why even take a dog in a shop with you any way? Just tie it up outside.
Get a real dog, not one of those play things!
If there is no sign up saying you can't **** on the floor do you think you are by default able to **** on the floor?
If they tell you that you can't bring your dog in then you'll probably have to go along with that, they don't have to put a sign up to cover every possible thing they don't want you to do/bring into their shop.
Unfortunatly allergies, hygiene and many other aspects make it difficult to disagree with the shop owner.