If you are concerned about spam bookings then one of the things you can do is ask customers to complete a CAPTCHA code during the booking process:
From the Dashboard, click the Cog/Settings icon.
Click Dept Settings.
Tick the option Require customers to enter a CAPTCHA to confirm bookings towards the bottom of the page.
Please note that this will add an extra step in the booking process and some people may find Captcha codes difficult to complete.