Here is implementation documentation from Mastercard about l3: https://na-gateway.mastercard.com/api/documentation/integrat...

The cost reduction is very small, it’s applied to interchange fees. I’ve been directly responsible for implementing this functionality on payment gateways for multiple processors because it helps reduce fraud holds as well.

Separate question, what are your ethics around the surveillance of Americans' economic activities by private actors? What "rights" are relevant in this space and which do you subscribe to?

I'm not going to debate you about anything, I just don't get the chance to ask insiders any of these questions.

Do you think there are different ethical concerns when dealing with non Americans?

Also a great question.

My ethics are “this is unequivocally wrong without consent”.

Thankfully my work was on payment products that serviced businesses and government entities, so I did not really have to deal with that moral quandary.

However it gets muddier in other spaces as well. There are types of cards, like HSA/FSA that require something similar to level 3 data called IIAS that is used to determine what parts of your purchase are eligible. In the parts of the systems I have worked with, this is covered by HIPAA, but I have no idea if there are “clever” methods to sneak that data out of the chain elsewhere.

Is this data requestable via a GDPR takeout?

searching for “mastercard level 3 data takeout” and such bring up the same 5 pages that are not relevant.