Devon Trade Centre has been fined £8,000 for promoting misleadingly low prices on vehicles for sale on its website.
Owner Mark Hiscox was also fined £4,000 for the offences. Both he and the company, which pleaded guilty to eight charges, were also ordered to pay £3,148.45 each for prosecution costs.
The dealership, in Axminster, was prosecuted by Devon Trading Standards Service under the Consumer Protection from Unfair Trading Regulations 2008.
Customers reported being misled by low prices advertised on the business's website, when the actual price of the vehicles on the forecourt was much higher.
In addition, vehicles were also then subject to an additional administration fee of between £249 and £599.
One price displayed on the website was £1,500 lower than the price the customer was actually asked to pay.
Trading Standards officers had previously advised the company that advertised prices had to be true and accurate but the complaints continued.