What is the best way to show in-app purchase features to the user

Showing greyed-out features that are not available is a bad idea and not recommended by Apple in their design guidelines. I do not know if it is grounds for app rejection. You can certainly have a button labelled 'info on extra features'.

@ PBK Thank you for your reply, that helps - Just to clearify something, the features are not gray-out they are shown as normal, they just don't function as the user may expect, the only thing the user will see every time the try to use any of these features is pop-up message lettiing them know that it is a premium feature and they will need to purchase it before they can use it.

Where can I find the guide-lines as far as UI desing for in-app features (if there's any)?

Thanks

As a user, I only want to see interface elements that are actually functional at that moment.

(My second choice would be for non-functional elements to be clearly displayed as non-functional.)

Having something that looks active but only leads to advertising would be a major distraction from using the app in the first place.

@ pmills -Thanks a lot for your input, I tend to agree with you, that's why I was a little concerned.