He's a Traveling Man with a Hammer
If you hear a knock at your door, you don't even need to ask who's there. With door-to-door contractors, there's no punch line -- just a bad deal. This variety of contractor is notoriously untrustworthy. Door-to-door contractors are often seasoned scam artists offering unbelievable deals to hapless homeowners looking for cheap repairs. He may tell you he just happened to be driving by and noticed your house could use some work, or he has some leftover materials from another job he needs to get rid of, so he'll cut you a deal.
The truth is that if you agree to any of his offers, he'll almost certainly provide quick, shoddy work with cheap materials that will leave your property in a more serious state of disrepair than it was before he came knocking.