Consumer Protection said fines were handed out to the Fremantle site, as well as one in Narrogin and another in Victoria Park, for charging customers more than the amount reported to FuelWatch or displayed on their price boards.
Consumer Protection acting commissioner David Hillyard said it was disappointing and unacceptable.
“Consumers need to be confident that prices reported to FuelWatch, and subsequently published on the FuelWatch website, are accurate,” he said.
“Clearly, drivers make petrol purchasing decisions based on this information and should not arrive at a filling station to find the true cost of fuel is higher than they were led to believe.”
Petrol sites need to notify FuelWatch of any price changes, with the reported price to stay in effect for 24 hours from 6am.
Changes need to be reported to FuelWatch before 2pm the day before for them to take effect.
Locals who want to report overcharging or the wrong price being displayed are asked to call |1300 304 054.
Visit www.fuelwatch.wa.gov.au for prices.