Only allow repeat customers to book online (support login)
Customers need to sign-in to be able to make a booking online. This means non-customers need to call or create an account.
Jeff Loucks commented
suggest people just need to enter email address to rebook. implement a check to see if the client exists already.
Daniel Bamler commented
I´d like to give groups of customers access to my booking calendar, so that they can pick available days to request trainings. Allowing only signed-in customers to be able to book would do the trick I guess. I thought of having a blocked requesters list could be a good idea, just in case someone is misusing the service to annoy a business owner by sending fake bookings. What's your opinion on that?