When can you engage with customers on social media? Only when they want you to.

One of the biggest mistakes businesses make on social media is to treat it as a customer acquisition channel when that's not what it's best at. So says Matt Goddard, CEO of R2 Integrated, a digital agency whose clients include Microsoft, Hershey, Aramark and Black & Decker. "We've been preaching pretty much the same thing for four or five years, that social is not a channel -- it's more of a behavior."

Social behavior goes back to the dawn of time, and its digitization is certainly important, but it's not as easy to manipulate as some marketers seem to think. "Where I think marketers are missing the boat is they think they can run social as a customer acquisition vehicle. Sure, you can pump out marketing messages as social posts," Goddard said, "but you can't insert yourself into what we call 'dark social,' the peer-to-peer networks, [which is where buying decisions really get made]."

Goddard has addressed this topic in a presentation to the American Marketing Association, and we're also talking to him as a potential speaker for the next E2 conference in Boston.

An array of social listening technologies for keyword monitoring and big data linguistic analysis of social feeds have sometimes been promoted as potential sales tools. But suppose you discover a conversation in which someone is discussing a buying decision for whatever it is you are selling. Does it really make sense for you to butt in on that?

"I don't think you can," Goddard said. "For every customer evaluating your product, only a small percentage of those going to want the brand to chime in. Also, the dirty secret is you can't scale it. For a large company, you're talking about hundreds of millions of interactions … and [you] would need thousands of people in your call center to actually butt in those conversations. It's not a place where brands can market at scale."

[ What trends do you expect to see in social business this year? Read 5 Social Business Predictions For 2013. ]

Note that this is an entirely different question from whether a brand should intervene in conversations where people are complaining about its product, or asking support questions about its use. If somebody's having a problem with your product, they are already part of your ecosystem, Goddard pointed out, and responding appropriately to those complaints or questions can be a huge boon to customer loyalty.

The R2 blog provides some good tips on other productive tactics, such as social media prospecting, which would be one way to apply the social media search techniques I discussed here recently. Another post covers the trend toward greater use of images in social posts as a play to grab more screen real estate and appeal to "window shopping" behavior on the web.

Where Goddard ultimately sees the most potential is the use of social media for product research. The closer people get to making a purchase, the more they tend to turn to those 'dark social' networks where they get more private advice from close friends, family or business peers. Still, enough is visible to give businesses a better understanding how their products are perceived and what new products might be brought into existence to serve unmet needs.

Because social media users listen to each other more than they listen to brands, offering them the right thing is critical. "Companies that have the best products are going to win. Those that don't have great products are going to lose," Goddard said.

Follow David F. Carr on Twitter @davidfcarr or Google+. The BrainYard is @thebyard and facebook.com/thebyard

Social media make the customer more powerful than ever. Here's how to listen and react. Also in the new, all-digital The Customer Really Comes First issue of The BrainYard: The right tools can help smooth over the rough edges in your social business architecture. (Free registration required.)