First and foremost, it's important to choose a web development company you can trust. You can begin this process by reviewing a web dev company's existing website. A company who takes pride in their own site may be more likely to take pride in developing your site as well.
Next, you may want to check out the company's work portfolio. Here, you'll be able to view what types of clients the company works with as well as the type of websites they build.
If you are impressed with a company's website and the work they've created, your next step is to take a look at reviews. Begin with testimonials listed on their website (if any). After that, browse popular review sites such as, Google Reviews, Yelp, and Clutch.