Never had an amex card, so I didn't know that. Wonder how banks treat infinite credit lines on their balance sheets.

Its not a credit card, its charge card

I don't suppose they worry, Amex doesn't allow the user to carry a balance, the bill has to be paid at month end, so it's not long term debt.

They also check each purchase based on your credit rating apparently; so if you try and blow the lot on bulgatti veyron on a $50k salary they are probably going to tell you to get lost.

The $300k guy must have a fairly high net worth as they say here.

I very much doubt that. I believe they validate against your history with them rather than primarily against external sources. I know that I was able to charge $20,000 in a month at a time when my credit rating was at the low end of "fair".

Which planet do you come from?

That is what I understand as well. The guy in question was an antique dealer and made 6 figure charges to his card several times a year.

No idea, but this is what they claim

(link)

I think it's account history that's critical. They never question my billing travel related items but did call me when I bought a car with the card.

That was the problem for me. It's a corporate card. I only use it for trips. I hadn't used it in quite a while because I hadn't been tripping. Then I made several largish transactions in the space of a few hours. Bells went off.

Easily sorted but I'll remember for next time to warn them.

When there's been a card issue they've called me on the cell and it's been resolved there and then, I've never had a transaction refused.

Not having a corporate card has served me well, I charge all manner of corporate stuff to my personal card and then get reimbursed; conveniently forgotting the taxable benefit of the points. Points which got me, and an American who seemed not to like you, to Australia and points which redecorated the bathroom.

Yeah. Though I guess the fundamental thing is that there are checks and it's not 'unlimited'

I think it is unlimited. In fact that's the whole reason for having it; I know that if I have to spend a lot in one month I don't have to make arrangements for that. It may be that unusual purchases, for me, get questioned but that's not a matter of concern; I just want to be able to rent more rooms and run up a bigger bar bill than usual if I feel the need.

The corporate card does have the benefit of my not having to deal with the bill. One does have to be crafty, however. Some things never go on the Amex. I never charge bar bills to the hotel room. I do spend a fair bit on taxis. I provide receipts, though, natch.

Well, given that amex can choose to limit what you spend if they wish I'll stick by my definition (though this may be an irrelevance to you)