Flood damage may be hard to spot, but a car that's been underwater will literally rot from the inside out. Flood damage can ruin electronics, contaminate lubricants and threaten mechanical systems, often without leaving outward signs.

Used-car sales are expected to top 44 million this year, so consumers should be on high alert for signs of hidden damage and potential fraud. To help you avoid cars with water damage, Carfax offers these tips:

• Check: Check the trunk, glove compartment, dashboard and below the seats for signs of water damage such as silt, mud or rust.

• Examine: Examine upholstery and carpeting closely; if it doesn't match the interior or fits loosely, it may have been replaced. Discolored, faded or stained materials could indicate water damage.

• Turn on: Turn the ignition key and make sure that accessory and warning lights and gauges come on and work properly. Make sure the air bag and ABS lights come on.

• Test: Test lights (interior and exterior), windshield wipers, turn signals, cigarette lighter, radio, heater and air conditioner several times to make sure they work.

• Flex: Flex some of the wires beneath the dashboard. Wet wires will become brittle upon drying and may crack.

• Smell: Take a deep breath and smell for musty odors from mildew.

• Visit: Go to a trusted mechanic for a prepurchase inspection. Always get vehicles checked before handing over any money.

• Ask: Ask to see a detailed vehicle history report. Carfax Vehicle History Reports can reveal many hidden problems from a vehicle's past, including flood titles, and will indicate if a vehicle has been titled/registered in at-risk areas during flood and hurricane seasons. If the seller does not offer a report, use the 17-digit Vehicle Identification Number (VIN) available on the dashboard to check the car's history at www.carfax.com.