Honestly I wouldn't do anything about it. The math equation to work out cubic feet is literally elementary grade stuff. If folks are crazy enough to buy those bundles(I sell them to from time to time), they can afford to pay whatever is charged. I'm like you however. I'm honest with the volume. I figured it out one time to be 900.00 a cord with the volume I was bundling. Just used a tire and and bailing twine with a cinch knot.
I think its crazy what people will pay for those bundles of wood, but even crazier is that my wife sells rounds that are 8-12" diameter and 6-12" tall for $12 each, and people often buy 10-20 of them for kids to play on. She buys them from a local mill for $5 each so I dont have to deal with them.
There should be a label on the gas pump with the name and maybe the number of the weights and measures inspector in town. That's who should be interested. Now he/she might only be interested in doing the gas pumps as part of their job, but they should be appalled and know whose purview this falls under.