Passengers have different personalities too. Some out going ones would talk and joke and congregate with FAs, in some people's eyes they must be non-revs, but they are not. Or some had been on the same flight before they might stike up conversations among themselves or with FAs, in people's eyes they must be non-revs, but they are not. Or samll group of people on company vacation or conference, they are excited they talk they laugh they swicth seats around so they can be together, in some people's eye they must be non-revs, but they are not.
A nicely-dressed woman sits quitely in her FC suite, keeps to herself entire flight, poeple may think she is on business trip, but she is not, she is an employee. A man wearing a tie doesn't talk to anyone just works on his computer for the entire flight, is he a businessman? no, he is an employee.

Above are my personal witness accounts. Unless you read the manifest, people are not always what you think they are.