From the article Attractive Things Work Better from DA Norman: Positive affect makes people more tolerant of minor difficulties and more flexible and creative in finding solutions. Products designed for more relaxed, pleasant occasions can enhance their usability through pleasant, aesthetic design. Aesthetics matter: attractive things work better.
In short: We have the tendency to place value on products/ services/ persons based on a very limited piece of data and we value things more when they cost more.
How attractive are your products? How good-looking is your website to your users? Attractive doesn't have to mean you have to spend thousands of dollars on a design agency. But you can't get away with throwing together some lines, forms and colors. If you're not a designer, get help of someone who is and make your shop look like it's very user friendly. The funny part? It'll actually become more user friendly.