They also dropped shingles on my wife's car.

I see nothing wrong with walking into the Brokerages you want to hang your shingle with.

Don't have any slick salesmen tell you "we need to replace all the shingles around the skylights and re-flash it!" 

Or you have a 15-20 year old roof that a serious wind storm tears off a substantial amount of your shingles. 

Is there asbestos Shingles, siding, tiles, etc.Other things that may be impacting the quote:1.

Currently looking for a tear off (2 layers) and shingle on a walkable roof, ~25 square.  

He even used dimensional shingles.

You can never remove all risk from these activities, my neighbor just two doors down recently had the whole roof cave in during a shingle replacement on a two family (it was condemned immediately) and it will be six months until repairs are complete. 

If your holding this property I'd invest in a better shingle so this is the last roof you ever put on that house. 

Last night it was extremely windy in my area and a roof shingle from the neighbors roof flew off and shattered the window on my building.