567392 Facebook coupon referral system

Looking for a facebook coupon referral system Here's how I would like it to work: 1) customer visits website to place an order 2) message on website says if customer shares coupon on facebook and *new* customer uses that coupon then customer will be given a instant coupon to use immediately 3) customer allows facebook app to post on facebook about website. Facebook post might say "I just ordered from WEBSITE. Click here to place an order and save as a new customer." 4) New customer clicks on facebook post, brought to website and either given coupon code or discount is automatically applied in checkout. 5) Other customer is emailed a coupon code and told in account that coupon available (another programmer will be doing this, bid is for Facebook app) That's about how I would like it to work, problem is I'm not sure how to ensure only *new* customers are given the discount. If someone posts it on facebook and a new customer clicks on it, then the someone that posts it can have that discount as many times as they like, but I do not want the same customers to be able to click on the coupon repeatedly and get a discount each time they order. Does that make sense? I don't know if we should track customers through a facebook app or try and track them through the website. Problem with tracking on the website is it is easy for a customer to create a new account each time so they could just create a new account again and again to receive the coupon. On facebook... I'm not sure how that works, would a facebook app keep track of them, even if they removed the app, would it know that they previously installed it if they installed it again? Winning bid will be working with another programmer who built the shopping cart and will be handling everything on the website side of it. I need someone for the Facebook integration.