Free -vs- Purchase App for iPad/iPhone question

I need some help/clarification on how the paid vs free works. I have an App and I have a free version with ads. When the user purchases I want to disable the ads... that's no problem. But, how do I know they purchased? When the user goes to the App store, to purchase do I get an e-mail, or anything that I can key off of? I do not want to have two versions and if I开发者_开发技巧 do, how does Apple evaluate both? I am ready to submit the App, but I am confused on how I transition from free to paid.

I hope this makes sense and someone can clarify the process for me.

Thanks

You could use inApp purchase or compile a different version that will have a price and sell it separately.

@Helge is right. You can do it either through In-App purchase or a separate app version.

If you want to knw about In-App purchase pls go through this Tutorial