If you know what a wrench is and can remove a bolt, you can definately change your own oil. The fact that the oil filter is SO conveniently located makes the job THAT much easier. You don't even need to jack-up the car to get to the oil drain plug (bolt)....at least us skinny guys don't
Save yourself $20'ish and try it one time.
As for the overfilling, the only thing I can think of is that the shop is not allowing a complete drain of the oil. OR, your engine is one that takes a smaller amount of oil for some reason (pending that your dipstick is reading correctly).