Yes, you can refuse a Sailsquare user's booking within 24 hours, after that period his/her reservation will be automatically confirmed and can not be canceled.
However, we remind you that you're always entitled to refuse a reservation if personal information entered by the user about age, sex and nautical experience is partially or totally incorrect.

Also remember that overbooking can not be considered a reason for refusing a reservation; it can happen that some users book without contacting you first, but keeping the spots constantly updated is a way better solution.