Recently we had a problem with duplicate charges with worldpay because we retry after 7 seconds, but some of them were actually still processing after 7 seconds, so dupes. If this is a potential problem with any other processors (i.e. they don't do any rate limiting or dupe detection) we should see if we can't make the audit parser alert. In the case of worldpay, 2 charges with the same order number is a situation unique to this issue