Maybe there's something you're not seeing. My local Chevron, being at the crossroads of a posh neighborhood and another we ordinary folk live in, posts the prices it charges if you use a credit or debit card. The price is 10 cents/gallon less if you buy with cash and the air pump is free. That's still more expensive by a few cents than up the the hill across from the local high school where they charge you a quarter to use the air pump.
Ha! I bet there's more than meets the eye, but I too have often felt confounded by the dueling gas stations. If you find out why, please let us know!
Welcome back. I enjoy your Paris blog posts. I live in California and one of my daughters is putting down roots in DC. Planning an escape to Paris for December. I find DC so foreign from Cali. it is a delight to visit. I find the more you travel the bigger you home is. I know feel at home in all 3 places. C