You would probably walk out of that business and never return again. This is the very same with a website. If it is slow to download, or the information is not complete or easy to navigate to, then people will simply not return to it again. Considering the investment that is made in designing web sites this can prove to be a tremendous waist of what is potentialy a very powerful tool. Web sites need to be designed to be consistent and easy to navigate.
Information needs to be complete and upto date.
A Web site represents your business just as much as your employees do. When people walk into your business they expect good service. The same applies to the business web site. It needs to be helpful, have the ability to provide all the information that may be required or allow for information to be requested. If information is requested its no good responding several days later, a response is required as soon as possible.