“Error 404: Page Not Found” is a good sales tool actually. Your visitor already visit your web site. Making use of 404 page to direct them to other pages in your website. You can use the following search engine optimization techniques to attract customers.
1. Add some keyword rich content for the 404 page. For example, “Thank you for visiting ABC company. We are sorry you landed on a missing page. But you can find our product information in …”
2. Make the look and feel of the customized 404 page match your main site, likes color, style, menu, navigation, etc. Menu and Navigation are important because visitor can visit your website easily. This will help keep your visitor stays into your website.
3. Create a link to the site map page if available, and make the link easy to find. This will help your visitor to find information in a quick fashion.
4. Put your product information there. You can provide short description to introduce your product. It will be better to provide a direct link to the product page there.