I have been taking Amex for 5 years.  In some ways I preferred it - they paid faster than VISA and MasterCard.

Their customer service for merchants has never been good - clearly their policies are the opinion of the person you are talking to, and sometimes you have to keep calling back until you get someone who will listen.

Recently, however, much worse, as I found out.

In September in Florida, we got clobbered with hurricanes.  I write software and had a lot of down time.  One of my clients ordered a huge software package right before the hurricane.  He was warned that, if we were hit, that would delay delivery.  He said ok - had it right in his email.

Sure enough, we get hit while I was creating his package, he has a delay, his software is late.  Unfortunately, this software was for resale (which he didn't tell me) and he didn't explain this to his client, who bails on him.

So he received my software when the power comes back on, and a month later wants his money back.

No way - you got what you paid for.  So he calls Amex.

I dispute his charge back, show our policy, tell them what happened, and his chargeback is denied.

So he calls again to re-introduce the charge back.  This time the woman tells him to say that the software doesn't work (I know this because he gloated over this in an email to me), which he does, and then the woman immediately grants him another chargeback.

So I call in - well, we are sorry, but if the software doesn't work, then we give him his money back.  How do they know it doesn't work?  Well, he told us.  You can sue him if you think this was done in error.

Now we get to their chargeback policy:  

Step 1: hold up the money
Step 2: try to get the same amount that they already have out of your account.
Step 3: If the money isn't in your account, try to get it three times a week FOR A MONTH
Step 4: A month later, when you have been chaged $90/week, just as if you had been bouncing checks this whole time, take the money they have been holding, and release the funds they have collected from AMEX your clients during this same time, and which they have been holding while they try to charge your account.

What can you do?  Nothing!