...then the Arabs came and they bought Mercedes Benzes...

Can someone explain this to me without using the phrases "raping the public", "because they think we're all stupid", or "they fuck you at the drive-thru"?

Why is it that when gasoline companies (Shell, Mobil, Marathon, etc.) hear about a potential increase in cost a few weeks off, they immediately jack up their prices? It seems odd to me, simply because when we all hear about a potential decrease in cost a few weeks off, those prices never drop immediately because "that cheaper oil still isn't here yet?"

I ask this knowing that my request is impossible. There's no way to answer this question without using one of those three phrases excluded above.