Hi!
There is this rare case that can happen, specially in Events: when the last unit of a product or event ticket is being bought by two different customers.
When Customer A and Customer B start the buying process, there is only ONE unit available, but they don't know that, of course. While Customer A checks out and pays and get his confirmation properly, Customer B checks out, pays... and system fails saying there are not units available. But it's too late, as the payment has already been made.
I haven't seen this case in the whole forum, so if anybody has any idea how to handle with this, I'd be very thankful :)
Thanks!