You are mistaken only in that it is likely far more common than you think for corporations to do this kind of stuff. The people at eBay just got caught because

You are mistaken only in that it is likely far more common than you think for corporations to do this kind of stuff. The people at eBay just got caught because they were egregiously poor at doing it covertly. Companies have long employed internal and external private security forces to silence their critics and threats to them. The Pinkertons have been doing this in the US since the 1850s, for example, which predates almost of every form of state intelligence services.