Like that latin phrase goes... 'Quis custodiet ipsos custodes?' (meaning 'Who will guard the guards themselves?'), have you ever thought who trains the corporate or freelance trainers themselves?
(pic credit: http://cheko111.deviantart.com/)
Now that I have some of your attention thanks to the deviant artwork by Mr. Cheko111, let's actually look around a little. Trainers, trainers everywhere. Where do they get trained?