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We won't delve into complex human–computer interaction theories here, but rather try to make sure that your shop is accessible to as many potential customers as possible. Your ultimate goal should be to have visitors trust your shop enough so that they star start buying.
Every time a visitor stumbles upon a usability problem, your site loses their trust. Ultimately, if the trust reaches a low point, frustration comes and the visitor leaves your site, without buying anything of course. Such is the importance of usability in the e-commerce world.
When design designing your shop's theme, keep in mind that its mission (in addition to selling goods, of course) is to show your visitors that your website is managed by serious and competent people.
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