The importance of relevant content
One very important feature that is missing from many websites is relevant content. A website can have all of the other SEO related features in place, but if the content is not relevant, people will not stay. Not only that, but they will never come back.
If you are driving people to your site in the hopes that they will find a way to troubleshoot a car problem and when they arrive they see only car parts for sale, they will most likely leave because parts is not what they're looking for at this time. They need to know whether or not they need a replacement part and, if so, which part they will even need.
However, if your site gives them troubleshooting tips and offers them the replacement parts for their problem, you now have a resource on your hands where people will stay and most likely return. This is the type of result you should strive for on all of your websites.