Facebook and MySpace might finally pay the price for the big social gaming scandal: At least one law firm is investigating whether to launch a class action suit on behalf of duped users.

Sacramento-based Kershaw, Cutter & Ratinoff, LLP is looking for people who faced "unauthorized charges imposed on Facebook and MySpace users who participate in social games like 'Farmville' and 'Mafia Wars.'" The firm, which said it has launched an investigation into such scams, specializes in class action suits, among other areas.

Mike Arrington's TechCrunch has posted a series of articles on the issue of sleazy revenue models for online games, exposing the practice of sneaking mobile data subscriptions and pricey "learning CD" packages past players trying to earn online "points." Mafia Wars and Farmville creator Zynga gets a third of its revenue from such "commercial offers," while Facebook in turn gets 10-20 percent of its money from Zynga, according to Arrington.

Zynga has yanked some of its ads; Facebook, in turn, has suspended one of Zynga's smaller games. But there's evidence this issue could have been addressed much sooner. TechCrunch found video (below) shot this past spring in which Zynga's CEO said he "did every horrible thing in the book to, just to get revenues right away."

That sounded bad enough when it was reprinted on a tech blog; imagine how it's going to sound in court.

(Top pic: Zynga CEO Mark Pincus, possibly calling his lawyer, by Joi Ito.)