No tips I am afraid but a friend of mine once went to an interview where a David Brent style manager said "I am now going to leave this room and call you on this phone and I want you to treat me as you would one of our customers". With that he proceeded into the room next door and called the phone pretending to be an angry customer. Due to a combination of being able to hear him through the wall and his ridiculously over the top angry voice my friend could not stop laughing down the phone and did not stop even when the bloke returned to the room. Needless to say he was not hiredl!!!
I would also laugh, I really am glad I am self employed!