the fact that they mounted your skis incorrectly is at the fault of the shop. Maybe they would refund you for the mount?
as far as keeping them there goes, looks like they mounted at the factory recommended line. Which means that the ski will actually ski better, the side cut and flex of the ski are relative to a factory mounting point, so the ski will function as it was meant to at that point. (usually means it will perform better all over the mountain)
center mounting your skis is for people who are skiing more park than piste and want their skis to work best in that zone. Meaning you get a better swing weight with center mounted skis, and more tail, which makes skiing switch, and grabbing blunt easier.