This hoax is usually run by driveway paving companies, whose materials—hot-top asphalt and concrete—can’t be returned to the supplier. So the crew pulls up to your house with a load of leftover product and quotes a great price to resurface your driveway on the spot.

Even if it’s really a bargain (by no means a sure thing), taking them up on the offer is risky if you have no idea who they are and haven’t checked references. And if the driveway starts cracking next year, you can bet you won’t find this bunch again.

How to protect yourself: Never hire a contractor on the spot, whether it’s a driveway paver, an emergency repairman who shows up after a major storm, or a landscaper with surplus plantings. Take your time to check contractors out to make sure they have a good reputation and do quality work.