better gasoline?

[Chevy454]

Here's what makes my head hurt...I can understand the supply/demand thing in regards to the refineries and prices, but the thing I don't understand is the way gas stations themselves play with prices. They seem to raise/lower them at will, regardless if they've gotten a new load. I live in a town of only 600 folks, and we have 3 stations in town...my front porch is literally within 100 yards of one station, and the other 2 are within an 1/8th mile...so I know exactly when they get their loads of fuel. But, their prices rise and fall each time you turn around. I get the fact that if you get a load of fuel and it costs the station *more* than the last load that the end price will have to be adjusted to reflect the same profit margin, even though they have fuel left in their tanks that they may have bought for 20 cents less...and while they're usually slower to react to getting a load of gas cheaper, the converse should be true. BUT, how/why do they get by raising the price when they're working on the same load as yesterday, or last week? Shouldn't the end price reflect the same profit margin? The speculation part of the formula should only come into play at the opposite end of the spectrum in the futures market...am I missing something?