We get fuel price updated early every morning from GlobalAir. The iFly GPS App will automatically pull in the new Fuel Prices and FBO data each time you are online. However, most Fuel Managers do not notify of these price changes, so aparticular airport may only see 1 or 2 updates in a month. That is why AirNav has "Guaranteed" prices and the rest are as updated.
We actually ran a accuracy check on GlobalAir and they are very close to 100LL and Airnav at the time. They have a team that emails and contacts airports for fuel prices, however they do not contact them everyday, nor do they automatically know when they change their price. It may not update until the next cycle or email.
A crowd-source in an option to improve that is on our wish-list, but would need a verification methods... Or better yet a "fuel hub network" to allow all fuel managers to report once. Again GlobalAir was very close in accuracy and the pricing was conducive to offer it as an included service. We considered going with Airnav or others, but there prices are astronomical and it would need to be a paid service at that point. Definitely on our radar to improve accuracy even more.