WARNING: Breakfast is not included. When entering ...

WARNING: Breakfast is not included. When entering breakfast area, they will ask for your room number. I didn't think anything of this since most hotels include breakfast. Went to checkout, and was charged 19 Euro! It's not like I ordered from a menu and they served me. It was the same self service as other hotels. They should have told me at check-in, or at entering breakfast area. It's a tricky practice, and I won't return just for this reason.