Your arrival window is two hours wide, and the technician phones when about 15 minutes out. Before the sink cabinet is opened, shoe covers go on and floor protection goes down. Emptying that cabinet ahead of time helps, since the disposal, its wiring and the dishwasher hose all sit at the back.
Nothing under the sink is touched until the technician has named the failed part in plain English and quoted the whole repair. Say yes and the $89 visit is credited to that quote. Parts and labor on that repair then carry a 90-day warranty. If the disposal turns out to be past saving, you hear that just as plainly, with no pressure either way.