Smokers can take a hit of up to £2,000 ($2,700) when they trade in their cars, according to HPI, a U.K. vehicle-data and valuation specialist.

The two main drags smoking has on a vehicle’s value are physical damage to the interior and smell, something many smokers often are unaware of or think can be eliminated by using an air freshener, HPI says in a news release.

“Smoking in cars is bad news as far as resale health is concerned,” says Fernando Garcia, the firm’s consumer director. “The first thing a car dealer will do when looking at a car being sold by a smoker is knock down the price of the part exchange. That’s simply down to the fact that a car for part exchange has to be made fit for resale, and this becomes considerably more difficult and expensive when that car was previously driven by a smoker.”

Cleaning the car can cost up to £150 ($201) and still is no guarantee that the vehicle will smell sufficiently fresh, he says. “In severe cases, the internal fabric and head cloth may have to be stripped out, too – a process which can run into hundreds or thousands of pounds, depending on the extent of the smell and the type of vehicle.”

Also pulling down trade-in values is the cost of repairing any marks, stains and cigarette burns to the dashboard and upholstery.

“Some dealers tell us they won’t even buy cars from smokers because of the time and expense of getting the cleaned-up car properly clean and ridding the interior of unpleasant odors,” Garcia says. “Unless consumers want to see the residual value of their vehicles literally go up in smoke, I’d urge them to try to quit or at the very least refrain from smoking inside the car when driving.”

HPI issued the news release ahead of Stoptober, the U.K.’s 28-day stop-smoking challenge that runs until the end of October.