Generator Mix-Up

The generator company is here now and was supposed to service the generator and put in a new part - the thing that basically runs the generator (which they knew about 2 weeks ago when we called them.) They are here now and the guy had "no idea" he had to bring any part. He is servicing the generator now and has to order the part and come back, but says we don't have to be home for him to come back - of course we have to be home - to make sure the generator kicks on once the new part is put in since I don't want the first time we realize the new part doesn't work well to be when the power is out and the generator doesn't kick-in.