Even for those of you who don’t play Zynga’s Facebook games, if you’re on the social networking site at all, you’ve definitely heard of them. Because you’ve probably seen a lot of updates like this: “Jane found a sad, lonely black kitten on their farm! Oh no!” or “John just conjured up a few too many salads in Cafe World!” Though one you probably won’t see is “Jim just got scammed in YoVille!”

Zynga is the company behind FarmVille, YoVille, FishVille, Mafia Wars, Cafe World, and others. These are games that work under the increasingly popular business model that lets you play for free until you get really hooked and then need to give them some money to get better stuff. In FarmVille, for example, $5 buys you 7,500 “farm coins,” which you can use to get more game content.

Recently CNN was speculating that Zynga might be preparing to go public, since the games seem to be, well, everywhere. And referring to allegations of scammy offers, one analyst noted that they need to “clean up their act” or that plan might be dead in the water due to a tarnished brand.

The potential scams come in the form of other ways you can get those farm coins besides paying for them directly – like signing up for trial offers. Or you know those “quizzes” that you take, and then they send you results via text message on your cellphone? Well, you might want to look real closely at your cellphone bill the next month.

These advertisers are all third parties, and not all of them are scams, obviously – but it was enough to get Zynga in the middle of a class action lawsuit. The named plaintiff claims that she lost $200 from the advertising offers she used to get more stuff in YoVille. For example, she signed up for a trial offer of green tea, and then wasn’t able to cancel the trial and wound up with over a hundred dollars of products she didn’t want.

So is this Zynga’s fault, or should Facebook users know better than to sign up for these kinds of offers? And for those of you playing FarmVille or its brethren, have you paid for extra virtual cash or are you perfectly happy farming away for free?