Two factors determine whether a website will be successful - high search position and 'usability'. The first without the second means that a website gets visitors, but poor usability means that they are unlikely to do business with you.
The second without the first means that although it is effective, it's invisible to thousands of potential customers.
SEO Consultants Alone are not the Answer
They are not involved with 'usability' and have no interest other than getting traffic to your website.
Most Websites are Task Oriented
Websites do not have visitors - they have customers who should be treated accordingly.
To convert customers to clients, websites must allow them to accomplish their tasks effortlessly and
- have an understanding of the customer's needs;
- employ minimal, informative and persuasive content;
- demonstrate a pleasant, appropriate appearance;
- use navigation that is intuitive.
Nearly all websites fail. Traditional marketing favours 'engagement' but on the web, visitors need to get in, accomplish their task and get out in short order.
What Usability Studies Demonstrate
'Usability' focuses on the interaction between a website and its visitors and attempts to understand why visitors do what they do. It then seeks to remedy defects so that the website functions optimally. We have some books on usability here.