As an ex-AMEX employee, I can tell you most of the problems can be avoided by calling ahead and telling the CSR you are planning a large purchase. The ones that don't have any problems thus far probably have large or unusual spending patterns, and the computer doesn't flag their purchase as a potential stolen card. If you think about it, multiple purchases for $1000 even, all in a span of a few minutes, tends to look suspicious. Second point is that while AMEX has no pre-set spending limit, in reality, it is based on your ability to pay. An extremely large purchase immediately after your cut (billing) date can be a warning sign for people planning to skip out or go into a financial crisis (CCC or bankruptcy).