Adding custom fields in the Booking Preferences can be used to add terms & conditions that must be agreed to prior to completing the booking process.
Setup > Services > "Name of service" > Booking Preferences
Looking at the example below, the Field Label is shown in plain black text in the booking widget.
The text in External Link Name is clickable, in this case we have directed to the terms & conditions page on our website.
You must also select Yes for mandatory to ensure your customer agrees to your terms & conditions before completing the booking.