The price of gas is taking a big chunk out of everyone's paycheck, but how do you know you're getting all the fuel you paid for?

Inspectors in Georgia and South Carolina show up at gas stations by surprise to make sure you're getting your money's worth.

The overwhelming majority of times the pumps are on the money, but there are some cases: less than one percent in Aiken County in the last year -- that aren’t spot on.

"It's not good, it's already high enough, so why would they bill us more?" asked PJ Proud, filling up at an Aiken station.

The results are in -- and the pump might be putting a little extra squeeze on you. During the last year, state inspectors found 12 pumps in Aiken County -- putting out less gas than the customer paid for.

Names like Greg's, Kent's and Kangaroo Express all had a pump on the list. But they all say they're not out to rip you off.

"We try to give all we can for the money, the problem with the pumps is they're mechanical," said Greg Kendrick, owner of Greg's Gas Plus. "Sometimes they give too much, sometime they take gas."

He says people can also cause a problem.

"Typically after the pump is cut off, I have seen them drain the hose," Kendrick said. "(It) is really not their gas; it's for the next person."

He says there's simply no way to make sure the pumps, or the customer before you, are behaving exactly right. But in either case, we're just talking fumes here. Still -- he says he's doing everything in his power to make sure you get your every cent worth.

"All we want is to give the consumer exactly what they paid for," he said.

NBC Augusta asked Georgia and South Carolina for information on their inspections. South Carolina got back to us with Aiken County's information over the last year.

12 pumps out of more than 1600 inspected put out less fuel than customers paid for. Four pumps put out more.

And as far as Greg's Gas Plus -- just one pump was improperly calibrated -- out of more than 150 inspectors tested.

See the raw data