I heard today that there are websites that sells fake doctors' excuses to students or employees to use in missing class or work. I won't print the web addresses here but you could google for them.
I don't take documentation for missing class...instead I give my undergrad students the equivalent of one week in a 15 week semester that they can miss for any reason. Any additional absences result in a loss of participation points.
When I went to one of these websites today, I found three misspelled words on their homepage...maybe the author should have gone to class!