iOS Detect Purchased Version to Change Functionality

Is it possible / allowed to detect one version a user originally purchased my app? Or conversely be able to detect new purchasers?

I am switching the app from paid to free and adding ads however ideally I would be able to detect those users who've already paid for the app a开发者_开发问答nd not add the ads.

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As far as I know it's not possible. Detecting and not charging re-purchaser is as far as I know 100% on Apples side.

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The best way to accomplish what you want would be to have a free version in addition to the paid version. Anything else would be fairly error-prone.