The margin and the fee are measured differently
Fuel margin is cents per litre. The card fee is a percentage of the total sale, including the fuel excise and GST you never keep. On a large fill, the card cost can be a meaningful share of the margin on that transaction.
That is why rate negotiation matters more here than in almost any other retail category, and why the shop basket is often what actually earns.
Pay at pump is pre-authorisation, and it has its own rules
Unattended pumps hold an amount before the sale completes, then settle the real figure. How that pre-auth is handled, released and priced varies by provider, and it affects both cost and customer complaints about held funds.
It also means the pump terminals are unattended equipment, with the monitoring and settlement questions that come with anything nobody is standing next to.
Fuel cards sit outside the card schemes
Fleet and fuel cards run on their own arrangements with their own economics, separate from Visa and Mastercard interchange. A quote that only addresses scheme cards has only addressed part of your traffic.