That's why I post videos of my mpg. Takes the BS out of the equation.
Driving style can account for a 30% difference in mpg. Some people have no idea how to drive, some people are 100% throttle or 100% brake with nothing in between. Some people don’t use cruise control on the hwy and are always tipping into the throttle to make up speed they lost due to inattention. Some people drive around with 20 psi in their tires. Weather and terrain play a part. There are dozens of reasons for variety in reported mpg besides lies, but logic isn't as much fun as trolling. :)