Have each prospective company describe how they plan to evaluate the effectiveness of the finished project. In the answers provided, look for them to mention tools like analytics, conversion rate optimization, and search engine results. If your prospective website company doesn't have a plan for keeping and improving traffic to your site, throw out their RFP. No matter how good your new website looks, if no one visits, you've wasted your time and money.
Training And Ongoing Support
Most new sites require some amount of training and ongoing support, especially if you plan to make your own updates. Define your expectations for training sessions, materials, and ongoing support after launch. You don't want to be forced to rely on your web development company to make simple changes
Key Staff And Company History
Knowing the team and company's history can help build trust. A company with a proven track record is more likely to deliver results. Have your prospective vendor provide a brief history of their firm, as well as bios on the key personnel at the company. Have them describe their previous experience in providing services to other companies similar to yours. Again, if you're close enough, a company visit would be a great idea. Some companies like to leave the impression through their website and marketing materials that they have a large staff, but the reality is most of their "employees" are freelancers, leaving them with limited control over production timelines, quality, etc.
Knowing the staff involved can also provide you valuable insight into the type of agency they are. Some are staffed more branding and design, while others are more technical and staffed by developers. It is important to make sure the agency you choose specializes in all aspects of web design and development.