This makes the shopper's job easier. If you make him or her write down product numbers to fill in on an order form, you are not taking advantage of the Internet's benefits. If you sell many, many products, customers can get lost. You want to make it as easy as possible to find and purchase from your site. If customers have specific requirements, a search engine can help them find what they want and eventually buy it.
Frustration is the usual response.
You never want to give a customer that has already made the decision to buy a reason to leave. Many sites use the same navigational menus on every page of the site so customers feel that no matter where they are in the site, they can always get to where they want to be. Pleasing Design Real-world merchants take great pains in making their stores clean, neat, pleasant places to be. While you might not notice how clean a real world store is, you'll definitely notice if it is dirty. Besides making your site look good, a good design can instill confidence in customers.