The scenario you are describing is not really valid. However, if a
Buy or Amazon order is somehow modified without our involvement after
we have retrieved it from the marketplace, our system will not be
aware of the change. As far as I know, this doesn't really happen, so
it should not be a matter of concern. We only retrieve orders from
those marketplaces after payment has cleared and the order is
essentially ready to be fulfilled.
Regarding eBay, it is not unusual for us to retrieve orders before
payment has cleared, but when that happens, we will retrieve an update
later on.