Open the car door and the stench is enough to knock you off your feet. Mold has started to bloom on the doors and there is still water in the cup holders. Three weeks after floodwaters in Houston have receded, evidence of the flood is everywhere — especially in the cars the storm left littered along highways and roads.

More than 500,000 cars are estimated to have been flooded during Harvey, and incredibly some of them may end up in an online ad or a car lot near you.

At McCree’s Ford in Dickinson, more than 1,000 vehicles flooded. “All but nine vehicles,” said Mitchell Dale, McRee’s owner. The new cars will be crushed. Used cars will be sent to salvage. Still more customer cars, flooded in the service department, await their owner’s insurance company to come decide what’s next.

It is the salvage and under- or uninsured vehicles that can often end up cleaned up and offered for sale several states away. Salvage cars are supposed to have titles that brand them clearly as such. But as Adrian Cortez, a special agent with the National Insurance Crime Bureau explains, “These documents are either altered, or they may be taken to other states in an attempt to wash that branding off of the title.” Under- and uninsured vehicles may have flooding that is never reported.

An unsuspecting customer on the other side of the country might not have flooding at the top of the mind and miss the signs that often stay with a flooded car, despite the best efforts of crooks to clean them up. Cortez says to look for corrosion in the engine and sediment in odd spots. Lights that look hazy might be a sign of previous flooding. And then there’s that smell — it’s almost impossible to get rid of. Lift up carpets and run the air conditioner. Check the trunk and spare. Cortez says always have a reputable mechanic look over a possible purchase before buying. You can also check out a car’s VIN on their website.

Back at McRee’s, despite the estimated $35 million in losses, Dale feels blessed. None of his family or his employees were harmed in Harvey’s floodwaters.

“The real sad part is how many people’s lives were impacted,” Dale said. “Our cars can be replaced.”

Fox News' Casey Stegall and Maggie Kerkman contributed to this report.