One of the main reasons of double bookings (or overbookings) is having your property listed on multiple distribution channels at once. So you can get a reservation from Airbnb, and in case if your inventory is not in real-time sync with other channels, you can get an overbooking from Booking.com or Expedia.  It happens because you need time to close the rooms in another channel. It's even more important during the nighttime or peak season. Effective Tours offers nearly instant (few seconds) syncs between all of the connected channels.