There is a gas station in my town that charges 25-30 cents more per gallon for gasoline than all the other stations in the area. I never see a lot of cars there but there is often at least one car filling up there.
Do their customers know that other stations are less expensive? I'm sure they do. Why do they gas up there? I don't know. Is that a rip-off and is it illegal? I don't think so. Different sellers charge different prices, and some buyers are knowingly willing to pay a higher price at times, for whatever reason they want.