We usually skim reviews before buying or downloading apps from the App Store™, but getting an accurate story is difficult to impossible. Many app makers manipulate their reviews and ratings in one way or another — they bribe users, purchase positive reviews, or use subtler tactics. How do you really know which reviews are genuine vs. ones you should ignore?

In our efforts to offload this labor to apprecs.com, we've analyzed millions of reviews and developed a classification scheme.

At the top tier are the most trustworthy, and at the bottom are the least. Let's start with the ones we consider to be generally untrustworthy, pictured in red.

Aggressively Requested. These are reviews that result from the app excessively nagging the user for positive reviews. Users will often post a review to get the app to stop hounding them and leave them alone. Such a practice becomes obvious when the reviewer points it out, though a high frequency of very short reviews can also be a clue.

Filtered / Cherry-Picked. At the next level are filtered reviews. For such reviews, the app asks for users' opinions and then asks only those users that responded positively to post reviews. The other users — those who expressed negative opinions — are not asked for reviews. This system serves to cherry-pick reviews and skew the app's overall rating in a positive direction.

Network-Sourced. Below that level dwell the reviews from a network of some sort. This could be the app developer's personal network of friends and family. It could be an online community where the developer has requested reviews to boost the app's ranking. Or it could be a review exchange network, providing tit-for-tat reviews ("I'll rate yours if you rate mine"). On the surface, such reviews can be virtually indistinguishable from organic reviews, but many can be detected by looking for similar review patterns across multiple reviewers.

Reward-Driven. One level down lie the incentivized reviews. These are the ones where the app users expect to receive rewards of some sort for posting their reviews. Apps may promise to unlock a feature, dole out free coins or gems, or give some other bonus. You're not exactly given cash to post a review, but you're given something else of value, and you might have otherwise have had to spend money to get it.

Paid. Way down at the bottom, in the bowels of review purgatory, are the paid reviews. Be they from a review mill in China or from, say, a fiverr freelancer, they're driven by a pure cash motive, most certainly not a selfless desire to spread truth.

Apple's policy dictates that developers not attempt to manipulate reviews, but it's clear that that's often not the case.

The most trustworthy reviews are the ones that users write spontaneously, without any incentive ("organic" reviews). Unfortunately, they can be very hard for apps to acquire, and reviews or the lack thereof can make or break an app.

To cope with this, apps often employ an occasional request for an objective review. Though reviews triggered that way might not be quite as unbiased as spontaneous ones, this practice appears to be allowed within the App store, and it can serve to counteract the phenomenon where users with negative feelings are more vocal than others.

Reviews are vital to an app's success, and it's very difficult for honest app developers to gain a foothold in the app market when they must compete with other app developers that violate that 3.10 guideline. Furthermore, biased reviews make it difficult for users to discover the absolute best apps.

Earlier, we mentioned the technology we developed to filter out untrustworthy reviews. To try it out, go to apprecs.com/search. We'd love to hear what you think on Facebook, Twitter, or elsewhere.