Start with the basics. Check the website and make sure it has information, completed projects, examples of their work, and a list of the services they offer. Then book a consultation. You're not required to sign a contract during the consultation if something doesn't feel right. I was lucky enough to find an affordable interlocking contractor in Woodbridge - OAKS Home Services, without any recommendations. I found them myself. I think they're a good contractor because they clearly explained the differences between the materials, what would last longer, and what made the most sense for my project. Basically, I had a good feeling about them from the very first meeting.