RV Fuel Issues & Prices - Post 'Em Here!

My feeling is that the price should be the same with the seller making the sale that otherwise he would NOT have gotten with cash. For example; I have $200 in my wallet. I'd like to keep my cash for emergencies so I use my card when possible. The gas station discounts cash or charges 10 cents ($3 for 30 gallons) for card users. So, I use the cash BUT I don't fill up. I only buy $50 in fuel, not $120 (assuming fuel is $4 and I'm buying 30 gallons) I'd think the seller would rather sell $120 for a credit card user than $50 for a cash user.
Hope that makes sense...