@Maria901
You will be penalised in a number of ways: a financial penalty against your next booking, your calendar will be blocked so that your month long guest won't be able to book those days anyway, and a note published on your reviews that you cancelled on a guest. Plus, you will be barred from being a Superhost for 1 year. The guest will get all their money back if you cancel - but is it really worth doing so. Sound like you are focused on the short term rather than what this could do to future bookings when potential guests see a cancellation on your reviews.