先加油后付款 or 先付款后加油 make a big
difference to gas station profitability.
profit magin of selling gas is very very
low so gas station rely on selling snack,
drinks, cigarette to make profits.
先加油后付款 usually lead to greater
sale of these non-gas goods. So unless
theft of gasoline is very prevalent,
gas station is reluctant to have a
先付款后加油.