If traffic don't convert, people are not stupid to buy again. Look at my stats at AdEngage and you will see a 75% repurchase rate.
FROM ADENGAGE
Repurchase Rate 75%: The Repurchase Rate is the rate of returning customers for a particular site. A high repurchase rate is a good indication that advertisers perceive high value advertising on the site.
http://www.adengage.com/create_ad.cfm?site_id=47831