As Ethel say, any trader has the right to decide to accept or refuse trade for whatever reasons they decide. (There are a few exceptions, relating to such issues as racial discrimination).
The filling station is within their rights to charge 'customer number one' 1p per litre and accept his cheque. They can then charge 'customer number two' one million pounds per litre and refuse a cheque. 'Customer number three' can be turned away because the proprietor hates people with roman noses. 'Customer number four' can be offered a sale, at any price the retailer chooses, only upon the condition that the customer has to dance stark naked around the forecourt for 24 hours before being served.
If it's your fuel (or anything else offered for sale), you have every right to determine the conditions under which you're prepared to sell it to someone else.
Chris