Now a days ipad, iphone and Samsung Galaxy smartphones are easily available. Users are using these phone to visit the website and buy the goods. Is your website is mobile compatible? make sure when you design your website its looking good in smartphone also. So if its not looking good then you lose your sales and traffic. Google also announces into each updation of algorithm about "mobile friendly" website.
All persons are going outside with their phone rather than desktop and laptop so most of time they watch websites in phones. So phone are most usable thing in public to watch the websites. Also speed of website should be tested because your website is open by lots of people in the world using different internet speed.
You can customize the website in low resolution and these are should be prefect visible in mobile and tablets. Also check your website CSS in all browser and mobile devices some are showing wrong and some are right, so compatibility is must in design. If your website is looking good in phones then you get more traffic and increase the sales. Most of popular websites have different version for browser and phones. Its good so they can easily watchable and reach to the users.