my guest didn't read the terms very Well And asked me to cancel the booking because he does not want to pay the additional cost for cleaning, towels etc.
what Can I do to cancel without cost for either of u's?
Under no circumstances should you cancel, nor should you accept an email off that seems like a penalty free option rom the guest for you to cancel.
Tell the guest that unfortunately as they made the mistake they need to contact AirBnB and explain what has happened and see if they can switch their booking to a more suitable property. This means they don'\t lose their booking fee either