I read the following sentence in the news story about a disabled Carnical ship drifting due to an engine fire.

Passengers also are getting sick and throwing up, he said, adding that his wife told him: "The whole boat stinks extremely bad."

It is quite common in AmE to use expressions such as the above, or saying "smells real bad" instead of "smells really bad".

How to know if a particular expression/sentence is just wrong, or if it is acceptable?

Thank you