In fairness I do cover shifts more times than not, because deep down I am just a yes man. I may refuse initially but my line manager knows that if they follow up my initial no with a "its just someone has phoned in sick and were desperate" or something along those lines I will immediately relent and say yes. The only reason I ever say no is because whilst I am at university it is really hard to also do night shifts. Juggling Uni and work with two different sleep patterns is pretty difficult haha. But thanks for the advice, it is this reason I do try to help out as much as possible because I find that when you have a good employer, and you do favours for them, they will return it in some way!