This detection rule flags users who attempt to scan a receipt that has already been scanned. This can weed out "Dumpster Divers"; users who collect and attempt to scan discarded receipts.
The Threshold no. of re-scans can be Set/defined in the provided field under the mentioned rule. It can be found under the "Activity Detection Rules" in the "Settings" section on the dashboard. Please find the screenshot below. 
What does the "Scanned already used receipt" activity detection rule mean?
