Most of the time its down to the wording in the booking process, there a few things you can do...
- Change the message that shows once the form is submitted. Make it sound stricter. something like... "Thank you for reserving your date, your booking is being held for the next 30 minutes, and may be deleted if a deposit is not received" - this can be changed on the "translate" page under "customer messages"
- Set a Scheduled Notification email to go to the customer 1 hour after booking if no balance has been paid saying. "Your booking reservation has been scheduled for deletion as no deposit has been received - please log into your account here to pay your deposit and secure your booking"
- Send yourself a Scheduled Notification email or SMS 1 hour after booking if no payment is received with the clients phone number or email so you can follow up manually and request payment.
Then, if all that fails - delete or cancel the booking.
We've only had it happen ourselves a few times, and 9/10 times when we follow up, there's been a problem with their card or bank balance, and they want to speak to someone to pay with an alternate method.