You can do your own due diligence fairly easily when choosing a roof contractor or any contractor for that matter.
Due diligence should go beyond simply asking for references. A good contractor should have some positive references they can supply to you but this should not be your sole research tool. Who is really going to provide you with a bad reference? Follow up, call and verify the reference to make sure it's not just a friends phone number. It's a good start that a company is able to provide some positive references but your due diligence shouldn't end there.
Most industries including roofing are required to have certain things in place and they are easily checked and verified by the customer.
1). WSIB - you don't have to be registered with WSIB or have an account with them to check the status of a contractors account. You simply go to the "e clearance" section on the WSIB website and type in the name of the contractor and it will show you whether or not that contractor is "eligible for clearance certificates" If it shows they are not eligible for clearance certificates then that means their WSIB insurance is not currently active. There could be several reasons for that including a late paid premium which can be easily remedied but it's always a positive thing to see the account is active and in good standing.
2). General liability insurance - a reputable contractor should be able to produce a liability certificate proving they have active liability insurance. To obtain a liability certificate from the insurance company is no additional cost to the contractor and should be kept on file or on hand same as you keep your insurance and ownership in your personal vehicle. It's no more complicated than that. So ask to see a certificate.
3). Safety certificates - in certain industries the ministry of labour has required that individuals go through specified training programs and have passed a test obtaining their certificate for that field. As of October 1st 2017 anyone working over 10 feet from the ground must have their working at heights certification. This certification has replaced the previous fall stop and fall arrest programs which were all very similar. The workers must carry their certificates on them at all times.
4). Product certifications - we have touched on this before. It is extremely important that the installer is certified by the shingle or product manufacturer to install the components they are installing. You need to verify this and not just take it at face value. If they are not certified you will not get a written registered warranty from the manufacturer and should the product be defective it is important to have this warranty. You can verify this easily with the manufacturer either online or by phone. No one is certified by all manufactures as the manufacturers won't allow that so if you are told a contractor is certified by numerous manufacturers of the same type of product it's most likely false. Yes most shingles install the same way but regardless of proper installation or not you will have no extended warranty without using a certified installer. We are listed with the manufacturers of the products we install in the areas we service such as Orillia, Barrie, Midland, Gravenhurst, Bracebridge, Huntsville, Muskoka, Simcoe or Georgian Bay and that can be easily verified.
Basically you need to do a small amount of leg work if you want to ensure you get what you believe you are paying for. It's never good to go with the cheapest price as there's usually a reason it's cheaper than everyone else. Use common sense and listen to that voice in your head if something doesn't sound quite right. Take the few minutes it takes to check things out and satisfy yourself your contractor is reputable.