From the truck side:
Meters for retail sales (Which is what a consumer is) must be calibrated once a year, same as gas pumps.
Typically* when meters go bad, they go bad in favor of the consumer.
*About 80/20 in favor of the consumer, as the way most* mechanical meters work is small gearing. These gears spin on a tiny shaft, either parts of the gears come off, or the shaft wears down, making the meter turn slower, giving you more product. The only other way around is if something is wrong with the inlet of the meter, giving it a higher pressure but less volume, thus spinning the meter faster while delivering less product. In a product such as propane - I'm doubting this is very common. The only meters I really see this on is meters for water based product, as they rust up.