The garage interior was painted over 20 years ago when the house was near new.

Now, I want to remove some things mounted to the walls and get it completely repainted.

There is over 20 years of dust accumulation.

I don’t see much obvious dust, but the walls can’t be very clean after these years with the garage door opening and closing

How should I tell the painters to prep for repainting?

They powerwashed the exterior walls the day before the house exterior was last repainted, but drywall can’t get wet. Do they just put primer over the not super clean walls?