Scrub is the term that people use with credit card processors and their fraud/risk detection systems.
When a processor is said to be 'scrubbing hard', that means that they have tightened their rules and are accepting fewer cards based on their risk rules. When they are scrubbing less, it is generally easier for sales to get through.
They look at things like Time of Day for the purchase, country issuing the purchase request, compare card details, past history, credit card authorization data, bank, etc. There are many other things that they look at. Then, their risk management software returns a score -- and that score is compared against the threshhold for that merchant, and if the score is low enough, they take the sale.
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