As a merchant you either accept credit cards or you don't there is no limit to or time you can say I accept your credit but not hers.
I tried to purchase a soda and was told that Riverside Exxon had a 3.00 minimum for me to use my credit card. I explained to the clerk that I was filling up on the pump outside and was well above the 3.00. I was told, "that doesn't matter the minimum was per transaction".
I immediately stopped the pump and left this poor excuse of a gas station; I have a F-10 that holds 22 gallons and I was on empty when I started. I stopped the pump at about Â½ full, this is the last dollar Exxon will ever get from me. This 1.50 soda cost them about 40.00 more dollars today and you can statically figure it up for the next 20 years or so.