There are also many cases where the IRS investigate "service industry workers", where tips are the norm. This is because it is understood that those service workers will make a certain % of their income via gratuties. In fact there have been cases in the past where gratuity income was assumed, even when it wasn't declared
This happened to a friend of ours when the new rules came out (quite a long time ago). She was a waitress (and not very good at it
) at a popular steak house. When the paychecks came out after the first month she owed
the company and the IRS money! Needless to say, she found another job.