I'd agree with you on your assessment. He was just bottom fishing and indeed trying to eliminate the commission for the extra days as well as any local taxes.
I wouldn't do it; it's a violation of Airbnb policies and if Airbnb finds out (which they can by looking in your inbox), for any reason, they will deactivate your listing and probably not even tell you.
Colleen: I am new at all this, as you can probably tell, and my first instinct was to report him, but I don't know where or how. AirB&b's website is convoluted and somewhat circular, and finding any given thing is time-consuming. If you could shortcut that process for me, I'd be most appreciative. Thanks!