For brands on Facebook, spam blocking is a complicated matter. Because brands want to remain open to fans and allow them to express their love -- and sometimes hate -- for the product or company, the evisceration of spam turns into a fine-tuned effort to differentiate between millions of real and unreal fan posts, photos and comments, forcing companies to invest hours a day into cleaning up the brand's page. That's a lot of time -- and time equals money.

Indeed, Facebook has been improving anti-spam efforts -- just recently adding several new reporting and filtering features -- but the world's biggest social network does not give brands any special kind of spam protection. And while Facebook announced that spam decreased on the network by 95% in 2010, a quick check of some brand pages exhibits some ripe examples. Dr Pepper's page, with more than 8.5 million fans, displayed seven "add me" sexy-girl photos in a row, a free iPhone offer and a chain letter threatening years of bad luck.

For brands, page spam isn't just a nuisance -- it can tarnish a brand's image and, worst of all, make their fans hit that unlike button, and fast. "A brand won't necessarily get in trouble with consumers if a spammer sends an email with a fake of the brand's logo," said eMarketer analyst Kimberly Maul. "If that same spammer posts a link or content on a brands' Facebook page, it's probably more likely to draw a negative reaction from consumers, provided the spam posting isn't dealt with promptly."

But what slows spam deletion for brands is the fine line between a fan and a spam. For example, one Ford Motor Co. page post looked suspiciously like a bad link -- the text read "Amazing Website!" -- but turned out to be a foreign automotive magazine. So Ford left it up. Similar nuanced decisions must be made when it comes to what Facebook management companies like Vitrue and 22squared have identified as spam for their clients' pages -- profanity, derogatory and inflammatory language, hate speech, and promotional items from their fans for products and services not related to the brand. Vitrue and 22squared found that, if analyzed in those terms, as many as 15% of posts may need to be deleted.

Vitrue, which manages accounts for MTV and its 20 million fans, has released a study, defining Facebook page spam as "posts and comments that a brand would find not suitable, appropriate or potentially offensive for their page and community." This definition adds hours to spam detection and removal, because often only a human, unlike an automated filter, can choose between spam vs. fan.

Buffalo Wild Wings' director of media, Paul Freher, said his company, which has 4.5 million fans, has to constantly decide whether to delete posts. "For instance, because we're a bar, we have DJs and event promoters participate on the page," Mr. Freher said. "So if they've done an event at Buffalo Wild Wings once or twice, they may come back and say, 'Hey, I'm spinning tonight' but it's at another venue, we check the users' posting history. If the last 17 posts they had were promoting their last 17 shows, then we'd remove them." But Mr. Freher added that it's a case-by-case basis. "If someone is doing a fundraiser for firemen, they're welcome."

So how long does all this take? "It's definitely a couple of hours a day," said Colleen O' Connell, HarperCollins' director of online marketing for children's books. "It's part of our customer-service role -- identifying potential spam, then researching. It's difficult. You don't know if they're a real fan, and if they are, you want to keep them engaged. So we evaluate their relevance." Ms. O' Connell said her division manages about 100 brands across Facebook, including books by Shel Siverstein and the "Chronicles of Narnia" series. Ms. Collins said many self-published authors like to use her companies' pages to promote themselves -- and unless it's relevant to the page, it's spam.

Companies that don't have the resources to invest hours a day conducting delicate spam surgery can hire agencies that will do it for them. Teams review flagged wall posts for a large part of the work day. "The first thing our team does in the morning is content assessment, reviewing the wall post or photo directly," said 22squared SVP David Rollo. "Anywhere between 30 minutes to two hours in the morning of culling through the conversations and filters we've set up as well as manually looking at the page two to three times per hour throughout the day." Mr. Rollo said that of the dozen brands that his company works with -- including Buffalo Wild Wings and Baskin Robbins -- all use a management tool provided by firms like Buddy Media or Vitrue.

An added layer of work comes in the form of legitimate customer complaints that are full of "f-bombs," Vitrue CEO Reggie Bradford said. Those fans can't just be deleted and banned -- they have to be passed on to the brand's customer service department.

Time and effort and a human eye: That's what it takes to run a spam-free Facebook page.

It's hard to put a price tag on this kind of effort. There's no standard dollar amount for a service that didn't exist a couple of years ago. Since contracts between brands and Facebook management companies and/or Facebook software providers depend on the size of the job, pricing can fluctuate, but it's important to differentiate between those two separate services.

Some companies like Vitrue and Buddy Media provide software that brands can use for various Facebook page activities, including setting up a filter to flag possible spam. That service can cost from $2,500 to $25,000 -- or more if an account runs multiple brands with multiple pages -- a month. A second service offered by a different set of companies such as 22squared review the data to see which page conversations are spam and which are fans, and funnel the messages to the proper department within the brand's company, be it customer service or marketing or legal. This service can cost anywhere between $5,000 and $20,000 a month, with variations dependent on the depth of service.

The costs of dealing with spam add up quickly. But with Facebook becoming more and more essential to a brand's image, can companies afford not do do it? Remember, TV commercials cost millions to produce and millions more to place on the right channel and the right show -- and while they don't produce spam, neither do they offer the kind of open, two-way communication between the brand and its consumers that is the bread-and-butter of Facebook pages -- which are free.

The reason large fan-base pages are so attractive to spammers and self-promoters is because of the exposure the spammers can get, even if their message is up for just a few hours. Ford's social media manger, Scott Monty, has noticed this growth, but along with it comes an added advantage -- fans are working as moderators of spam on pages dedicated to different Ford cars. "As we continue to grow our fan base, the issue of spam becomes more prevalent," Mr. Monty said. "But one of the most helpful elements of leading such passionate communities of Ford advocates is that even if we're not able to monitor the site in real time 24/7, we have fans who reach out to us and notify us of spam."

Virgin America, with a much smaller fan base than Ford, has noticed the same kind of enthusiasm and willingness to help. "We're fortunate in that we rarely have to do much -- if any -- moderation. Our fans and followers are a passionate bunch," said Jill Fletcher, Virgin's social-media manager.

But once Ford and Virgin America hit millions of fans, they're going to need some extra help with Facebook's special version of spam.