martinibuster - 1:05 pm on Jun 6, 2013 (gmt 0) [edited by: martinibuster at 2:15 pm (utc) on Jun 6, 2013]
Google already has filters in place to identify do-follow links from articles that are labeled with words such as "paid" or "sponsored." As far as I know, Google cannot algorithmically identify links from unlabeled but paid for articles.
There is a revenue model popular in the UK that is pay for unlabeled pay. Some sites hint at a required payment by disclosing in their writing guidelines that articles written by commercial entities will be considered advertising. But that's vague phrasing, not something obvious like a "Sponsored Post" label.
One way I can think of is to use data from confirmed link spam and identify sites publishing articles that link out to the websites in the group of confirmed link spammers, then penalize sites that have a high percentage of outgoing links to sites known to engage in article publishing spam.
If a certain percentage of outgoing links from a website are going to identified pay for play spammers or article directory spammers, then that website may fit the profile of a pay for play article publisher. Algorithms work with pattern recognition. So if a website fits a pattern then the website is guilty.
Perhaps next time you publish an article on another site it might be useful to do an outbound link check to see who else they're linking out to, to avoid getting caught in an unnatural links sweep?
[edited by: martinibuster at 2:15 pm (utc) on Jun 6, 2013]