Visit their website. Do you like their look? Does the site load quickly?
Request information. How long does it take for them to respond? If they don't respond to a new client quickly, how long will you have to wait once you are a client?
Call them on the phone. Do you like they way they answered your questions? Did they make you feel comfortable?
View their portfolio. Do you like their work? Do they have experience working with businesses, not just non-profit groups?
Ask for references or better yet, call the clients included in their portfolio. Find out how the company was to work with. Did they listen to concerns and suggestions and follow through or do their own thing? How is their response time to changes?
How do they charge for updating a site? Is there a minimum fee just to open the site?
Do they know how to market a site? A website is a marketing tool and should be designed as one. Your website is not the place for a computer "geek" to showcase the new technology they just learned. The objective of your site is to SELL your product or service.
Meet with the designer. Is their appearance and manner professional? Are they able to explain the process in terms you understand?
Keep in mind the saying "You get what you pay for". Sure your niece could design a website for you, but will it reflect the business image you want? It may cost you more in the end to have a site redesigned, or in lost revenue.
"When we were first talking to you about designing our website, you told us that our home page would be designed so that it could be found by search engines. I just wanted to pass along a compliment, because you have certainly succeeded! When I try to find other churches on the internet, I'm often frustrated, because they are difficult to find. But, people searching for our church website can always find us at the top of the search results. Virtualtech does a great job with this, and it really helps us!"