Hi @David11304
Welcome!
Double bookings are a possibility. The sync times are different for Airbnb vs Vrbo and definitely could cause a double booking; especially if the listing is very active. Once you create the listing and sync the calendars it is never set and forget. You have to monitor it and keeps eyes on both calendars. Many Hosts have learned to "refresh" their Airbnb calendar as soon as a booking occurs and/or manually place a block on the opposite calendar until the sync catches up. If you would like more info on that...send me a DM.
The curious thing is the sync sometimes just stops working randomly? Each platform blames the other and sometimes you have to delete the link and re-sync several times to get it to work again. Sometimes that doesn't do it and you spend a week or so trying to get it resolved. In 2+yrs I believe it happened 3x to an Owner I worked with as Co-Host. Fortunately we noticed it wasn't syncing 2x and had no issues as we just deleted the links and set them up again and it worked fine. The 3rd time we caught it right away, but did result in a double-booking. We we were able to get one guest to voluntarily cancel for a full refund within the 48hr cancellation window. This was a few months ago and it took a week or so to get Airbnb to fix it (it was their link causing the issue).
Use caution with prep days and advance notice though. You have to manually block days before/after a booking on Vrbo, while Airbnb automatically does that for you and blocks the Vrbo calendar. Also for some strange reason Vrbo doesn't allow same day bookings, but Airbnb does.
I think most Hosts (without a channel manager) accept the risk and refresh the Airbnb calendar after every booking and manually block the opposite calendar until the sync catches up. I do think the risk is acceptable if you keep an eye on your bookings and pay attention to both calendars. Maybe some other Hosts can chime in here with their experiences with this.