This goes on quite a lot. I have suspected a number of African students of doing this. I spoke to a Kenyan woman who I suspected of being a bogus student at a IELTS exam. The woman looked nothing like the picture in her passport. She kept assuring me that she was the named student. When I went to speak to a colleague she ran off out of the building and disappeared into the city. I have also had a number of blatantly falsified qualifications handed to me by Nigerian students. Again on questioning the authenticity the students made a rapid beeline for the exit! When teaching in the UK I now ask to see each students passport and ID card before they enter the classroom.