In any business, people are looking for people they can trust.
Typically, they are first looking for expertise. And you've outlined some good points that might illustrate expertise.
But, they are also looking for integrity. This appears to be a serious issue for many contractors. Will you do what you say you are going to do, when you say you are going to do it and for the price that was agreed to at the start? You need to illustrate that you understand this is an issue.
Finally, you want to show that you care about your customers, that you understand that their web site reflects their goals and objectives and values not only to their customers, but to their family, friends, the community at large and the employees. And you need to communicate that you care because the web site is going to reflect on you.
Technical and artistic expertise is the most important, but caring and integrity are also important.