You’re almost certainly building your site on a laptop or a desktop computer. That’s how you see it and that’s probably how you access it. It looks great to you.
But that’s not how your customers are accessing your site. A majority of e-commerce sales are done on mobile devices now. But you probably know that. You shouldn’t stop your compatibility efforts by only optimizing for the latest iPhone model and leaving it at that.
There are many different mobile devices. It’s not just smartphones. Think of netbooks, tablets, and e-readers. All these devices come with all manner of screen dimensions that are in turn getting updated every other day. Many sites work perfectly on most devices. Most. Not all. All may not be achievable, but you should aim to get as close as possible.
Many sites solve this problem by having separate desktop and mobile sites. This is great; it works fine for a majority of smartphones and desktops. But those in the middle, tablets, phablets, and smartphones that lean on the smaller side get ignored.
Don’t neglect device and browser compatibility. Your sites may not work on every device. Some devices just aren’t compatible with the modern internet. But you should make sure your site looks good on as many devices as possible. Test and update constantly. A few hundred customers here and there can stack up to quite a lot.
Update and optimize your site for all the most popular browsers and the most popular devices. Do this until you get diminishing returns, then stop. You can easily achieve cross-device and cross-platform compatibility with the use of emulators. A good place to start is your checkout page. The last thing you want is a customer having to pinch the screen and resize a page that is too wide when they’re trying to give you money. Then you can optimize other pages.