Happens a lot. People take exams or even interviews for other people.
I was working on a project last year, installing PCs in Jobcentres in London and the south east. You'd get 4-6 members of staff sent to a specific site.
One time, we met up with the team leader early to go over the work ahead. He had a list of all staff attending and was pleased to see a familiar name. "Oh, Mo Lucas is with us today. He's a nice guy. I've worked with him before".
An hour later, Mo turns up. Unless Mo had lost several stone and shrunk a foot and a half, then this was not the same guy
Turns out it was his "brother"

And the guy had no technical skills either