Yeah they both mean "shop." The only difference is that you can only use "quán" for food and drinks while you can use "tiệm" for many different types of merchandise/services. Tiệm hớt tóc = Hair salon Tiệm sửa xe = Auto shop Tiệm giặt ủi = Dry cleaner Tiệm is a lot more versatile. Anything called quán can be called tiệm but not vice versa.

There is no difference,you can use both of them. "quán" is a word of Northern, "tiệm" is the Southern's word. You can also use " cửa hàng" "cửa hiệu" "hiệu" for a "shop"

Quán and tiệm have the same meaning, the word "quán" is from the north and "tiệm" is often used in the south.