Let me give this a try.

First, God bless vendors like Camsco and Loomis. The world would be a much poorer place without vendors like them.

That said,

I am not suggesting that anyone lose money on AMEX purchases. That would be silly. But surely there are ways to allow people like me to use AMEX and still make the money you want to make.

I've discussed online shopping this with some of my friends and people I work with. I don't know how many of us there are, but for a surprising number of us us shopping online is primarily about three things:
1. Getting exactly what we want.
2. Not trooping futilely from store to store looking for exactly what we want.
3. Not dealing with clueless sales people whose only desire is to sell us what they want us to want.

Notice that "saving money" is not on this list.

We are definitely not people who have more money than we know what to do with. But we are people who highly value our time. All of us are willing to pay a premium to save time. We're happy to pay for convenience.

Suppose I had gone to the Loomis site and discovered that I could use AMEX, but that would incur a $5 additional surcharge. Would I have bought the book? In a heartbeat. It's a no brainer. Is it worth $5 to me NOT to have to spend 30 minutes digging out the checkbook, searching for an envelope and a stamp, driving by the postoffice, etc. etc.

Suppose a number of exclusive AMEX users come to the Loomis site ready to buy. Some pay the premium and buy. Some are annoyed by the preium and don't buy. No matter what the numbers are, Loomis comes out ahead for this group of users.

We are third millenium online shoppers, hear us roar, in numbers too big to ignore.

And yes, I am trying to tell you how to run your business. But I'm just trying to be helpful!!