After major hurricanes like Irma and Harvey, consumers looking to buy a used car need to beware of flood-damaged vehicles. It's estimated more than a half-million will hit the market in coming months.

"There is a racket out there where people will buy these cars cheap from the auction, re-do them, and then try to pass them off as a reliable clean car," Toyota of Tampa Bay Service Director Gregg Willard said. "As a dealer, I'm very worried, so as a consumer, you should definitely be worried."

Signs of Trouble Inside

These vehicles can look OK on the outside, but damage is often hidden on the inside.

"Trust your nose," Willard said. "If you smell mold or mildew in the car, it needs an extra look to see what's causing it."

If you smell mold or mildew, it's time to look for places unscrupulous resellers won't spend the money to fix.

"Things I like to do, I'll pull up the floor mats and rub my hand, cause there's padding underneath the carpeting. Is it wet? Is it damp?" Willard said demonstrating. "If I feel moisture here, I'll start pulling up the plastic panels down the side and look for water marks or stains there."

It's also important to look under the seats for any brown stains or water stains on the foam padding. Willard suggested holding a small mirror up under the seats to help you see better.

"That's very important, because it's one of the last places they think to clean," he said.

New carpeting in an older car is another telltale sign of flood damage. It costs about $1,500 to replace carpeting in a car, so it's unlikely someone will do that, unless there is water damage.

"They're wanting to turn these cars so quick and get them out to the consumer before they can get caught. I expect to see these cars hitting our market in the next 15 to 30 days!" - Toyota of Tampa Bay Service Director Gregg Willard

Also, be sure to look for rust in key areas like door hinges, seat frames, seat brackets, and break rotors.

"It can happen pretty quickly, especially if floodwater has salt in it," Toyota of Tampa Bay shop foreman Matt Fuller said. "It can actually rust within about 8 to 10 hours."

Water logged

Another thing to check is the spare tire well of a car. If a car has been in a flood, sometimes they forget to clean that out, and it's literally filled with water.

"I've seen it where it's filled completely up," Willard said. "You could hear the water sloshing around in there, and I actually saw mosquito larvae floating in the water."

Also, be sure to open the air filter box under the hood, which can hold about a gallon of water. If the air filter is wet, that's a bad sign.

"Unfortunately, this consumer drove through deep water," Willard said showing us a damp, dirty air filter. "This car has been here a week, and you can tell by the weight and feel of (the old air filter), it's still wet."

If someone drives through floodwater that's too high, it can hydro-lock the engine, causing so much damage it must be replaced. (*Watch the video above to learn what can happen to your car if you drive through floodwater.)

A grimy AC condenser can also be an indication that a vehicle was sitting in floodwater or someone drove through high water.

"You can tell by the debris in the AC condenser how high the water level got. Normally it's pretty clean, with just a few bugs and things like that," he explained.

Electronic problems can be the toughest to catch, because they often don't happen right away. Be sure to turn the engine on and check all the electronic functions on the dashboard looking for any glitches.

Check the title

Flood damaged vehicles are supposed to be reported to the National Motor Vehicle Title Information system. Be sure to do a VINcheck on any used car before you buy it. The history report should tell you if an insurance company declared it a "salvage" or "flood" title, but unfortunately, that doesn’t always happen.

That's why it’s so important to know the hidden signs of flood damage. Here's a checklist to review:

• Damp carpeting under the floor mats
• New carpeting in an older vehicle
• Water stains or dirt underneath side molding
• Water stains, mildew on the foam under seats
• Spare tire well filled with water
• Damp, dirty air filter
• Dirt, debris in AC Condenser
• Rust on door hinges, seat frames, seat brackets & break rotors
• Electrical glitches

If you're in the market for a used car, be on guard and know these warning signs. Dishonest resellers don't waste any time getting refurbished, flood-damaged cars on the market.

"They're wanting to turn these cars so quick and get them out to the consumer before they can get caught," Willard warned. "I expect to see these cars hitting our market in the next 15 to 30 days!"