I would like to create a print ad network for online retail advertisers with the following features. The ads will be distributed as posters.
The printed ad includes a URL with a link to the ad network's URL, including the promo code: adnetworkname.com/T57
The potential buyer would then need to be directed to the retailer's site in order to make a purchase (I am unsure how to integrate this, since I will not be able to control the retailer's site)
The system has to be able to track which buyers make a purchase on the retail site (the advertiser's).
Should the promotional discount be given before or after the sale?
I do not want to get too deeply integrated into the order flow of the online retailer, however, I need some control over which buyer used a promotional code (ie. was directed from my advertisement) to make a purchase (without changing the code on the retail's site).
What is the best practice approach in this case?