Making sure that a company has done substantial work is an important factor when choosing who you might go with. Make sure they have a number of examples that show their work and their process, comparing those examples to what you want for your site. Knowing that the company has done a similar site to yours and has experience designing a website in your field is a huge advantage for you.
It doesn’t matter how flashy or creative a website is if it doesn’t get results. This is why case studies are important, as they provide the statistics and figures that show that this design firm will be able to let you profit off your new site. Make sure to look at those numbers before making your final decision.
In any industry, knowing the people you are working with and making sure you are on the same page is key to any partnership. Making sure that the staff of the company you hire will listen to your ideas, offer you honest feedback and can get on the same train of thought as you makes all the difference when designing a website. Meeting the staff and making sure the company is reliable should be one of your first priorities when choosing a company