This post originally appeared in our July issue of “Live Report from the Future of Marketing,” our monthly Post-Advertising newsletter. Subscribe for free here.

They’re but one of hundreds of sites that allow anyone to publish their review of a business, product or service to the world, but on July 15, 6-year-old Yelp celebrated passing the 20 million review mark.

By any calculations, that’s an incredibly impressive number, especially considering all of those reviews are volunteer contributions by uninvested everyday people like you and me. However, new research and scandals on other similar peer-review sites shows that there might be a bit more incentive behind these types of reviews than first meets the eye: Several hotels have been found to be bribing or reimbursing visitors for positive reviews on TripAdvisor; Google Places is reportedly being flooded with unfair reviews; and new research by Cornell professor Trevor Pinch has shone an unflattering light on Amazon’s Top Reviewers, who often write reviews after receiving free products through non-transparent relationships with producers. Of the 166 participants in Pinch’s survey, more than 100 said they always or usually reviewed free books that were given to them, and that “if they didn’t like a free book and felt they could only post a negative review they felt obliged to give the author the choice of whether or not they wanted that review to appear. Invariably the author declined.” The millions of Yelp reviews themselves have not always been a cause for celebration for everyone involved, particularly businesses listed on the site who felt positive reviews of their establishment were getting buried.

Should we be trusting online strangers to influence our purchasing habits? We all know that any content we consume is backed by some sort of an agenda, but it seems that the notion that you can trust online customer reviews to be impartial and fair has been completely undermined. Studies have shown that consumers do indeed trust online product reviews from strangers—sometimes even more than they trust their own friends.

But anybody with a keyboard can now freely give their opinion, and while there are systems in place on sites like Yelp to try to ensure that reviews are actually trustworthy, it’s hard to know who to trust these days. Sadly, people’s opinions can be bought and influenced for, well, as the Jamie Kennedy Experiment’s “Insta-Cooker Infomercial” once demonstrated, a mere $20 (even after watching the insta-cooker blow up in a man’s face).

Slate’s Garth Risk Hallberg described Top Amazon Reviewers as “a curious hybrid: part customer, part employee.” So it’s clear that we should be reluctant to trust these customer/employees without at least knowing their qualifications. Does this mean that consumers will eventually stop trusting reviews by strangers in this Wild West of the web, inevitably going back to trusting independent publishers and professional critics? Or are we simply entering into an era, for both print and online, where publishers are forced to make a bigger deal of their guidelines to promote their impartiality?

We, for one, feel that the latter is an approach that must be followed by any publisher intent on being trusted for their reviews, and the sooner the better.

What’s your take: How do consumer or media reviews survive?