[poindexter]

For about a year now, Costco membership cards are also American Express credit cards.
You can put your purchases right on the card.

[onyx]

Yes, I know, I have one, but it still has to be valid and it is pre-authorized by CostCo.

[onyx]

The bottom line is thus: CostCo is not about to get stuck with a bad cheque or an invalid credit card purchase in the stated large sums. The transactions, however fraudulent, had to be valid in payment. No CostCo employee or manager could possibly allow a multi-thousand dollar purchase to leave the store without first confirming either the validity of the cheque or the credit card.