@igloo:
It is why it is important to get the breakdown, then. I don’t agree with the people who say “well, you negotiated the price before the contract was executed”, that price was based on the original expectations of what the job would take, not what actually happened. As others have pointed out, in construction there are plenty of cases where a contractor can charge you more for things they couldn’t forsee, for example if they pulled off the shingles and found the sub roofing was rotted, they had no way of knowing that. I once had a driveway done that was concrete that we wanted to be turned into an asphault driveway, and when they broke up the slab they found that half the driveway was poured to 8" depth (standard slab is 4"), and in good faith I negotiated payment for that extra cost.
It should be the same way the other way, if the contractor finds the job was less than he thought, in good faith charging the original price would be both unethical and also a good way not to get many more jobs. It is one thing if you change the nature of the contract (known as a change order), contractors charge a lot for those, make a lot of money out of them, but this was a case where the contract was negotiated in good faith based on services rendered, and you have every right to question the bill. I don’t think the 1/3rd reduction was necessarily too little (I couldn’t tell you that even if I looked at your roof), but asking him to itemize how it comes down to price X is not an unusual request. He should be able to break that down, like as originally spec’ed it was a 4 man day job (2 men 2 days), and it turned into 1, and show you the cost differential (ie if they bill each person for a day at 200 dollars, the savings would be 400 bucks).
With insurance, it could be that because he originally billed it at 2 days, he had to pay for 2 days insurance, but he should be willing to show you that, explain it. If he bought 30 rows of shingles, and only used 7,he might say “I can’t return the shingles”, but the other 23 rows could well be used on another job where they use a similar type, so you at least know what to argue. Estimates are not done out of the sky, contractors looking at a job know how many square feet of shingles they will need, the ice dam material, nails, they know how long it should take and believe me, unless the guy just decided to hang out a shingle, they know, and if the job took significantly less time they know how to bill that out. I have seen situations like yours where the contractor pulled one of the older cop outs in the book, that the sub contractor was responsible for what happened and would have to give you a breakdown, but that is BS, in a job like that that is the main contractor’s job to break it down for you and also be willing to negotiate on the price, and if he doesn’t, then to me he is dishonest (and I am not speaking out of not knowing, 2 of my uncle’s were GC’s so I know how the business works, plus have dealt with it as a customer). If he can show you that at your price he was able to save 1/3rd by the job being smaller, fine, but you have a right to an explanation.If the guy resists, tell him your next step will be to call the state agency responsible for licensing contractors and file a formal complaint, it may miraculously open the doors, contractors hate when complaints are filed because it goes on their record and potential clients check that (or should).