As MacRumors points out, a forum member at our sister site TouchArcade describes that Apple has apparently changed its review policy and no longer allows users to write reviews for apps obtained with a promo code.
Forum member slewis7 described that he had tried to post a review for an app downloaded via a promo code but encountered errors and was then told by an Apple support representative that “it is no longer possible to rate or review an app if it was downloaded using a developer’s promotional code to prevent comprimising (sic) of the rating system.”
Another forum member received the following response from an Apple support representative:
It is no longer possible to rate or review an app if it was downloaded using a developer’s promotional code. You can review this app by purchasing it on a different iTunes account using something other than a developer’s promotional code, such as a Gift Card, Gift Certificate, or other payment options.
Other members who participated in that thread describe a variety of results in writing reviews for apps obtained with promo codes, indicating that there may be some other criteria involved such as the date the promo code was generated.
Promo codes are a resource that app developers often use to help promote their apps since they allow recipients to download paid apps for free. Apple allows developers to generate up to 50 promo codes per app release. Many developers give away promo codes in forums and through Twitter and other mediums in hopes that users who might not otherwise purchase an app will try it out and leave a favorable review in the App Store. Of course, positive reviews that aren’t merited can be misleading to potential buyers, a situation Apple may now be actively trying to prevent.
Apple has not released an official statement on this purported change though we’ll be sure to let you know if one is made.