Meh, grease on the pads ain't the worst(brake) thing I've seen. There was the guy who greased both rotor faces, on all 4 wheels. The woman who brought her car in complaining of a "crunchy" sound when she hit the brakes. Rotors were so thin you could see the fins through them. I've seen rotors worn all the way to the fins as well, but they were in another shop.
And my all time favorite: Same guy put all the pads in backwards... TWICE. Steel backer plate to the rotor, and pad facing the calipers.
That's just brakes. There's also backwards fuel filters, K&N filters so dirty they actually twist themselves closed, Trans. services with no filter(I serviced the trans., now it won't move??), trans fluid in the oil, and vice versa, gasoline in diesel trucks, and vice versa, and many, many more.
Many of these done by much older people who should have known better. I think I'd let a high school kid slide a little....