Apple has issued a reminder to developers that it will not tolerate use of third party services to manipulate app rankings in the App Store. "When you promote your app, you should avoid using services that advertise or guarantee top placement in App Store charts," the reminder states. "Even if you are not personally engaged in manipulating App Store chart rankings or user reviews, employing services that do so on your behalf may result in the loss of your Apple Developer Program membership."
This reminder could very well be in response to a well-trafficked post in Touch Arcade where an iOS developer revealed that an ad network guaranteed his app placement in the top 25 apps in exchange for $5000. This third-party service allegedly employs bots to automatically download the targeted app multiple times, automatically increasing the app's ranking and granting the app greater exposure to potential human downloaders.
8 of the top 25 apps were allegedly developed by clients of this bot service. If true, this represents a serious problem to the legitimacy of App Store rankings, and it's therefore no wonder that Apple is reminding developers of its aggressive stance on the issue.