I wouldn't liken tax evasion to letting someone use your apartment. I was really just speaking casually about how the situation would unfold. It's also a grey area since this is less of a sublet and more of a micro sublet (akin to letting a friend over for the night who buys you lunch in turn), which complicates the legality of it. Err on the side of caution I guess, but reading your lease agreement is obviously the best thing one can do.