May I offer in-game currency in exchange for user ratings and reviews?

You can't violate this guideline:

Apps should not directly or indirectly enable gifting of IAP content, features, or consumable items to others.

But 'to others' suggests that you can 'gift' a consumable item to the user themselves in exchange for the user doing something. You can certainly give the user a consumable that they could otherwise purchase through an IAP when they 'find' something or 'kill' something or get to a new level so why not when they opt to go write a review?

However, I think you can't gift the consumable to them from outside the app when they write to you saying they wrote a review - how can apple differentiate that 'gift' from an outside-the-app purchase?

You can ask the user if they want to go to the store and feedback on your app, but you have no way to verify they did so. They can push the agree button, get their reward all day long, and be you'd left with nothing to know they followed thru. Might want to see 'Content Codes' in the review guidelines as well.

Question is...are you trying to get reviews or find a way to harvest user info?

I'd just go the traditional route of running a timer that pops up a dialog asking if they: would like to go to the store to leave feedback; not now; dismiss

Be sure to put a button to review in that app's about/info screen.

Good luck.

Here's an idea for you.

Have the app generate a random number and call that the device code. Display that device code and remember it. in the app Tell the user to write a review and include their device code in the review. Create a website. Place the device code of all reviews (only the favorable ones?) in the website. Have the app parse the website looking for its device code. If it sees its device code give itself a special reward - 3 gold pieces or something like that.

Is this consistent with the guidelines??? Perhaps, perhaps not -

- You can't "use [your] own mechanisms to unlock content or functionality" but that does not apply to 3 gold coins that were otherwise available through IAP.

- "Apps should not directly or indirectly enable gifting of IAP content, features, or consumable items to others" - but is it gifting "to others" if it's the user who wrote the review who is getting the gift themselves - perhaps it's you gifting to them in exchange for the review. Unclear. You can certainly start the app with 3 gold coins and you can credit the user with 3 gold coins if they get to level 2 so why not credit the user with 3 gold coins if they write a review?