To replace the seal below the impeller, the entire water pump has to be removed. Did they reuse the old impeller or is a new impeller on the parts list on the bill?
You can put muffs on with no impeller and 99.9% of the time you wouldn't know the impeller is missing. On the water, different story and it would show up in a few minutes.
I work an hour drive from the shop and work during their business hours so I had a friend pay and pickup the boat during their business hours and no reciept. When he called me he said 850 labor, 250 parts, plus tax. I knew I was dealing with a bad shop so decided to just pay without questioning and enjoy the boat. Bad idea.