I worked for Amex, it was amazing how F’d up the Govt reimbursement process was.
A huge majority of the military people wanted to pay, but they just refused to pay before they got reimbursed.
On the other hand Microsoft Corp cards especially when the holder was .Indian and went back to India never ever paid.
I remember a Saudi Prince who had cranked a few hundred thousand on his card and got a charge denied at A strip club. He told me flat out that he had been insulted by this and would not pay until he felt Amex had suffered enough for his loss of face. (I randomly checked 5 years later, and no never paid )
You should write a book or something. I know there were a couple written specifically about AmEx. I always like to know those things.