The warmer weather can bring out home improvement scammers, and the Frederick County Sheriff's Office wants you to beware.   Corporal Greg Warner says these individuals usually visit communities, knocking on doors and offering their services. "They'll typically start with something to the affect that 'I have some leftover materials,' specifically with the sealing of driveways. 'I could make you a really good deal.' There's often several people there. They may often start doing the work before a price is agreed upon, and then they'll come up and ask for a payment," he says.

When it comes time for payment, they only take cash or a check. If they receive a check, they quickly take it to the nearest bank branch to cash it.

"We have two recent cases in Frederick County. One in March; one in April," says Corporal Warner. He says they use the same methods to try to get residents to fall for their scams. "That's been consistent in both of these recent cases. These people never called. They just showed up and offered to do this service."

Corporal Warner says most home improvement contractors don't operate that way. They're often listed in the phone book, and will come out at your request to make an estimate before any work begins.

Consumer groups also say before any work begins, you should get estimates from several contractors, and check out their references.

Corporal Warner also says contractors must be licensed by the Maryland Home Improvement Commission, and can present their license numbers upon request. "There's a criminal charge for acting as a contractor without a license, and that's almost verbatim what the charge is, and selling home improvements without a license." He says violators can face up to 30 days in jail or be fined $1,000, or both.

The Sheriff's Office says if you encounter these individuals in your neighborhood, call police as soon as possible. The quicker authorities get there, the quicker they can arrest these people.