The first requirement is design skills. A website must also be professionally designed so that your site accurately reflects your company’s style and reputation. This can make the difference between someone choosing your service or products over another company’s.
The second requirement is website marketing. If a web development company lacks experience and knowledge in SEO/Online marketing, your website may not have a chance in the search engines.
The third requirement is after service. Availability of your developer is very important to resolve any issue (s) you may face.