Experience as a merchant. If we give Amex reasonable evidence that merchandise was received and a chargeback is unwarranted, there is a chance they will find in our favor, whereas Visa/Mastercard take the consumer's side almost unconditionally.
I suspect this because Amex is better staffed in this area.
A company I worked with had a dispute with a client over charges (fee for services + restocking fee) on her Amex. Amex allowed the client to keep disputing the charge multiple times. If the charge re-appears on her bill she'd file a new dispute.
Amex also directly provision merchant accounts for accepting Amex (separate to normal Visa/MC accounts) so they control both sides of the transaction.
OK, Interesting, I haven't had the same experience, having won a few Visa chargeback attempts from customers that received merchandise as ordered. My experience is primarily B2B though, where there are credit card authorization and tax exempt forms involved. So, it's not like the customer can claim they can't recall ordering something, etc.
Based on what everyone else says, it's probably sample size. The number of people we have who buy something with their own card and then chargeback is pretty small for us (and it's usually in error).
This is reasoning by anecdote; your experiences are not a valid sample size with which to draw such general conclusions about the whole field. Look how many are saying the opposite is true, your experience is probably an outlier, not the norm.
I suspect this because Amex is better staffed in this area.