Coremetrics reported that average conversion (number of purchases to the number of visits)in United Kingdom is 4% (coremetrics.co.uk). On the other hands the maximum conversions in United Statest are more than 30%. On the site index.fireclick.com you can track the most important indicators about conversion. In January 2013 they were:
Conversion Rate: Global 3.40%
Conversion Rate: First Time Visitors 3.30%
Conversion Rate: Repeat Visitors 3.50%
Cart Abandonment Rate 72.70%
Usually conversion rates is highest for Affiliate Programs, come from advertising in search engines and organic search results. For online stores conversion rates is between 0,5 and 5%, but you should remember that data conversion relate not to real users but measure trends and changes. One visit corresponds some about 0,5 real user. Of course it’s depend on trade and type of online store.
So what have it consequences? For example when you have conversion on 30% level you should focus on increasing traffic than optimize online store.