When the content of your website is accessible to people with a visual disability it delivers a benefit to customers and to business. Its also a marker of the quality of the team behind the website.
If it was a bricks and mortar shop businesses would be forced by strict legislation to give access to disabled shoppers. Not so in the case of online selling where there are optional guidelines or an industry standard, Web Content Accessibility, also known as WC3
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Size and presentation, clean layout and the ability to toggle the size of the text are important features. Addressing the main colour schemes that affect people who are colour blind is similarly a simple yet effective measure.
From a business perspective it makes clear sense to accomodate the significant number of visually impaired customers who want the full advantage of buying goods online when their visual problems are accomodated.
Businesses benefit with the competitive advantage over competitors that are unable to do this. You please the customers and you please the search engines. More customers access your site from across more browsers and operating systems. The search engines rank the easy to navigate format more favourably. They are rewarding the effort that has been made to create a clean and well structured HTML document which is tuned to be easily read by search engine spiders.
Interestingly upgrading inaccessible web sites can require significant effort and be costly. It is better and more cost effective to start with software that was designed and developed with the purpose of being readable to people with disability.