I always do my own oil changes, but I am willing to let them do it since it's free. I have and will always check my oil after a change since I really don't wholeheartedly trust dealers.
When I first took delivery of my SECOND '12 Impreza, the technician who performed the pre-delivery inspection soiled the sun shade on my moon roof. They then tried to scrub it resulting in the felt getting all screwed up. I pointed this out and they said they would replace it. I ended up doing the job myself because I didn't trust a tech that couldn't perform a PDI without screwing up. The process for changing the sunshade requires the removal of half the plastic in the car. I wasn't about to trust them to do that correctly.