If a customer inadvertently refreshes the order confirmation page, then the same sale gets tracked multiple times. This can be stopped by following the steps below 

1. From Admin Dashboard, Go to Campaigns -> Manage Campaign

2. Click on your desired program to edit it

3. Scroll down and click "View Advanced settings"

4. Where it says "Minutes to wait before accepting a sale from the same IP", put a time period to wait. For example, 10 minutes as shown below.

Once the changes are made, if a customer clicks on your affiliate link and then makes a purchase, if they happen to refresh the "Sales thank you page" within the time period you specify, the sale will not be tracked again.