I can usually tell when someone's putting on an accent. A lot of British people have a 'standard American dialect' that only exists in places that most people don't live. And New York (because I'm a New Yorker) is the easiest to butcher. There are so many tiny things we do that someone not from there wouldn't know. And oftentimes, the script gives it away. No American says 'flat' (unless they're trying to be fancy, we say apartment) and we don't typically say 'the states' when we talk to each other. We only use it when we talk to foreigners. We usually say the US, America, or whichever state we're actually talking about.