No, sorry. If we were to give free credits to referrers each time a referred user purchased credits, we would have to increase the cost of purchasing credits - otherwise TrafficSwarm couldn't be a free service. Plus, we feel that it makes more sense to make buying credits as affordable as possible.
You do however earn credits each time your referred users open their browser. And if you upgrade to a Pro account you can even earn credits when they click on links on their Start Page - and commissions when any of your referred users upgrade to Pro.