What is double booking?

Most double bookings are a synchronization problem rather than a human error. Two systems disagreed about what was free.

One-way calendar connections are the usual culprit. A system that writes appointments but cannot see what you added by hand will offer slots that are already taken.

The narrow remaining risk is two callers being offered the same slot seconds apart, which is a timing problem rather than a sync one.

Picture a dental office on a Tuesday. At 10:02 the hygienist's coordinator puts a returning patient into the 2:30 slot, typing it straight into the practice software. The online booking page reads availability from a copy that refreshes every 15 minutes, and its last refresh was at 10:00.

At 10:09 a new patient opens the booking page on her phone, sees 2:30 as free, and takes it. Both people get a confirmation. Nobody did anything wrong, and the office now has two patients arriving for one chair.

Whoever spots it first has to call one of them and move the appointment. If it's the new patient who gets bumped, her first experience of the practice is being told her confirmed time isn't real. The collision came from a seven-minute window when the copy was stale, and a 15-minute refresh opens a window like that all day long.

You don't need the vendor's documentation to find out whether your booking connection reads as well as writes. Open your calendar and add a fake appointment by hand, called something obvious like TEST BLOCK, for tomorrow at 3:00.

Now go to every place a customer can book: the web page, the link in your email footer, the phone assistant if you have one. Check whether tomorrow at 3:00 is still being offered. If it is, that channel can't see what you add by hand. Every manual entry your staff make is invisible to it.

Wait 20 minutes and look again. A slot that disappears late tells you the connection reads on a timer. However long that timer runs is the size of your collision window.

Then do the reverse: book a test through the customer-facing page and time how long it takes to show in your calendar. Anything longer than a minute or two is worth raising with whoever sold you the tool. Your front desk is booking blind in the meantime.

Availability is read at the moment a slot is offered rather than from a cached copy, so what the caller is offered reflects the calendar as it is.

Google Calendar and Outlook connect directly and two-way. Connections through Zapier are a different shape, and the integration matrix labels which is which.

Buffer rules are the practical defense against the seconds-apart case, and they are worth setting before a busy period rather than after one.