Be careful what you link to or you might unwittingly become the spokesperson for a drum of personal lubricant.

At least that's the lesson multimedia producer, writer and University of Iowa teacher Nick Bergus learned after he posted a link to his Facebook page of a vat of personal lubricant for sale on Amazon.

According to a post on Bergus' blog titled "How I became Amazon’s pitchman for a 55-gallon drum of personal lubricant on Facebook," he shared the link for the $1,500 barrel and wrote, "A 55-gallon drum of lube on Amazon. For Valentine's Day. And every day. For the rest of your life."

He was shocked when, a week later, his friends started telling him that they were seeing his post show up as a sponsored story next to their newsfeeds. Sponsored stories are a form of Facebook advertising that turn your friends' "likes" and comments about brands into mini-ads that can be viewed from your Facebook profile.

In other words Amazon had paid Facebook to use Bergus' post as an advertisement for its site, even though he had posted jokingly about the product and hadn't genuinely recommended that his friends purchase it...