There is no such thing as being overprotective when it comes to your home and your finances. There are plenty of roofing contractors out there that are willing to bend the rules to simplify things for themselves, resulting in problems for you and your roof.
Solution: Roofers' Compensation is a type of insurance covering roofing injuries. If a roofing contractor has workers' compensation, any injured employees are entitled to recover expenses for hospital bills and being out of work.
Be sure that your roofing contractor has workers' compensation so that you are saved from the trouble and expenses of paying those bills yourself.
Problem: You hire a roofing contractor to fix a leak on your roof. One of their employees decides not to use proper safety procedures and falls, breaking his leg. The employee holds you responsible to pay his medical expenses because he was hurt on your property.
Problem: Your roofing contractor leaves your roof uncovered after removing your shingles. That night there was an unexpected storm. Water seeps into your home and damages your sheetrock, carpet, and some nice furniture.
Problem: You hire a new roofing company to work on your roof. A few months later you notice a leak. You try to contact the company but can't find their information.
A general contractor is legally able to install a roof without a roofing license if they have a general contractor license. However, there have been a lot of cases of general contractors branching out and installing roofs themselves when they lack the proper training.