I've heard stories of them taking a hole saw to the splash guard, putting 2 o-rings on the filter cover, not tightening the drain plug enough.What can they do during an oil change that is so bad anyway??? The drop the oil pan, drain the oil, stick the new oil in right in front of you, and rebolt it back up. And check your other fluid levels / oil filter.
DIY oil changes are just a good peace of mind for me. If you're competent enough, you won't have any trouble.