Floating Gas Price

US has different gas pricing system from Taiwan. Different gas stations have different prices, even stations with the same company name. Therefore, I always check some websites of the latest gas price before adding the gas. However, I have already made many stupid mistakes on finding the cheapest gas price. Last time, we drove in the rain, spending one hour in the neighborhood, but could not find a station having the price cheaper than what the station closest to our apartment had. This noon, there are two gas stations near my company, one has price of 3.19, and the other has 2.94. I checked the website that there should be somewhere costs me only 2.91, so I decided to try some other stations. However, I could not find a cheaper one, so I turned to the station of 2.94. The sadest thing came. I parked my car at the pump, sliding my credit card, and just before the moment I picked up the nozzle, the price was changed to 3.09... God dxxn it!