faces in advertisments

My roommate, Nevada Watt (the half Canadian  is an amazing silversmith. As of lately, i've been helping her put her designs on her website and we discovered something interesting. With the Ball caps she sells, people only buy them if there are faces in the photos people buy the caps off of. We tried taking photos of them backwards on someone to where just the back of their head is showing, but people wont buy them! this is an interesting consumer behavior because you don't realize how much the face in the advertisement actually plays into the purchasing of the product. I think that when people see someones face, smiling in the ad it is more personal to them, where if it is the back of their head they don't even notice it. there is no emotion or feeling in the photo.