I don't think the issue is people being polite. It's that these messages look similar to the legitimate fraud alerts that credit card companies and banks send.

I don't think the issue is people being polite. It's that these messages look similar to the legitimate fraud alerts that credit card companies and banks send. What happens if you don't respond to those? Presumably, the transaction will be blocked -- but can you be sure? It would cause me a lot of anxiety not to resolve the issue right away.