Just take your business elsewhere, if possible!
Pretty much, however, some retailers get a "very good" Amex rate but ONLY if they don't surcharge any extra for Amex
One business I know had this "deal" from Amex, 1.8% and VI/MC is about 0.7% now, but they charge a 1% surcharge for VI/MC and 2.2% for Amex.
Again, take your business elsewhere. I have walked out of a car dealership before because they would not accept Amex for the majority of the car purchase price.
Another dealership was happy to take the $80K on Amex over a few days transactions, with a 1% surcharge which I was happy with