Can you actually TRAIN a bird to let you pet him on the head? Yep. You can. Is it really so hard to believe when people train goldfish to swim through hoops and dolphins to do double back flips (on cue)? 

It's important to look at this training in a certain way: You are simply communicating to your bird through the language of training, what your intention is and that you do not mean harm. Eventually "petting" training becomes fulfilling and rewarding just by how it feels to the bird (those scratches on the head DO feel pleasant after all!) but the first key is to make it not scary. 

This is done with a combination of things:

• Not petting long enough for the bird to make you stop. (Stop before the bird makes you stop) small approximations aka BABY steps!
• Associating petting with positive reinforcement (a treat) 
• A SIGNAL of your intention. 
• If you are not at the point in this video where you can pet first, then give a treat, then try this method instead. It includes the distraction of a treat to be able to make that initial contact and that contact only lasts the time of the duration it takes the bird to consume the reward.