We use our best judgement. In my experience it's most often confused in babies because it can be difficult to tell at times. I do not get upset when they say

We use our best judgement. In my experience it's most often confused in babies because it can be difficult to tell at times. I do not get upset when they say my son is adorable even though I don't have a son. I accept the spirit of their comment and try to politely correct them with something like: Thank you, she loves to flash a good smile. Then I go on my way.