I'm a big user. I heard the commercial and then a friend got me hooked on it. In two years I've made about $550. I like to save it all up and then cash out once a year. The post above is correct. They will offer you (as an example) ten cents a gallon, but will charge the gas station (as an example) twelve cents. Gas Station will buy into it as it will get the upside customer at their station vs the nearest to them station.
I have 1 account with my cards, my wife's cards, and my high school sons card on it. They text me when and where they fill up and I go in and claim it, by now they now the stations that accept it and fill up there. Smooth transactions.
However- here is my conspiracy- I am fairly confident I am correct. It is a GPS activated app. So the app knows when you are sitting in the gas station. If you pull the app up there is an increased chance you are only getting two cents vs ten-fourteen / gallon. I am absolutely convinced. I claim the app in my work parking lot and drive there I get the bigger payout. I forget and claim it in the gas station parking lot.... yep one cent or two cents. EVERY TIME. Naturally Upside will still charge the gas station the fourteen cents and make the profit. SO claim the station before you arrive.