On my first day of class I like to have the students introduce themselves right after my introduction.  This is a good ice breaker and gives me some information on the students as well.  They may seem nervous and shy but making them speak outload to the group often eases nerves of a new class and new faces.   Also I give them alot of my background information and experience in the field.  I found this to solve the doubts of my qualifications right from the start and since I was also an adult learner they  can see that if I can do it so can they.