If an Illinois resident does not want to be scammed by any type of contractor, the first place to check out is the website of the Illinois Attorney General.
It tells you exactly what to do in order to determine if the person trying to do business with you is legit or not. (I know, don't laugh!! But it's true!!)
Before I ever hired a contractor, I checked to see with the Illinois Attorney General's office how many court cases that company had against it in the past, and also pending. It's a free service that office does. Especially with roofers and window companies.