Your visitor should see that you care about a nice and clean look and feel for your site.
In real life you surely would not like to go to a ugly untidy site. And so it is on a web-site.
For shops it is even worse. You want people to spend money for the goods you offer and you need their trust. They will only buy if they can have trust in the quality of your goods and the service you offer.
They will ask them selves:
„Will I ever receive the goods I order in this shop?“
„Will I run into problems, if I don’t like the goods I ordered and want my money back?“
„What will happen if something is broken and I need the vendors service?“
Your visitor should see that you care about your shop and your visitors. You will not have the possibility to talk to your visitor. Everything the visitor sees is your site.
So keep your site clean and good looking.