DIN settings can be set differently and still be the right settings. The shop calibrates the binding to the forces indicated by your required setting. That you are a '6', lets say, on the chart doesn't mean your bindings will release at the appropriate force when set to 6.
That said, rather than reduce forward pressure to get the correct release values, the DIN setting should be changed. Only after all possible DIN changes have been made should forward pressure be considered to help the binding release in the proper range. He is right about the forward pressure marks, although in the middle of the range is what I strive for.
Loose screws are never good and if they were loose the shop may have neglected to glue the screws when they were mounted. Glue also seals the binding holes to prevent moisture from potentially damaging the ski.