Reveal Tab with Unique content based on location

Lots of marketing articles suggest using a 开发者_StackOverflow中文版coupon as an incentive in a reveal tab, but I don't see how you would prevent people who have liked your page from abusing the coupon by accessing it over and over.

In my app, I want to offer a coupon that the user sees only the first time they like a page. Users who have been to that page before would not be able to access it again.

I also want to limit who can see it based on location.

When your iframe fan page is rendered, Facebook sents an HTTP POSt to your page with a signed_request post parameter. If you decode it, you will get details about whether they like your page and what country/language they are from. If country works for you, then you are all set for that part. Restricting the coupon to only being viewed is not possible based on the anonymous information Facebook sends. You would need to create an application and have the user approve your application so you can get their ID and log that they have seen it. This would also give you more detailed information about where they are located.