Under construction law, once an unforeseen problem occurs, the job stops and a change order is created to cover the extra cost and scope of the new work.
A pool contractor gives a price to dig a hole and make a pool. But when he learns that 3 feet under the surface there is granite or some unforeseen rock that will triple the cost to excavate further, that will kill the project unless to customer is super rich and doesn't care his pool will cost an extra $250,000 to just dig the hole!
So when a retrofit contractor makes a jester not to increase the cost because of plumbing or electrical, this raises a question. Are they really good and have done this so many times that a small problem costs to resolve makes no difference because the contract price has lots of profit built in?
Take the case where I was adding a room onto a home. The sewer line didn't go to the street but under a hill and to the street behind the house. So to run a new sewer line from the rear of the house to the street in front of the house and to tie in, cost would run $80,000. To run a new line from the back yard to the connection under the hill, $130,000. But for me to run the line thru the next door's yard and to a sewer connection on a side street would cost me $15,000, plus a $25,000 payment to the neighbor--total $40,000. So when my client wanted no guess work but a firm price if I have to re-locate the sewer, I said $80,000 for a new line to the front yard and $130,000 from the back yard under the hill to the rear tie in location. But I can do it any way I want for a fixed price of $60,000.
So the sewer line had to be moved and I did it for the $40,000. The client didn't want to pay me the $60,000 even though I saved them $20,000. So the permit was in my name and I had the easement from the neighbor so I could cap off the line.... With no sewer connection the owner couldn't live there and would have to pay another contractor $100,000 for a new line to be run.
So in other words contracts and agreements between a contractor and client are on shacks ground. Owners never want to pay a penny more and even when a contractor wants to give the change order at cost, an owner will try to NOT pay any extra amount.
In your case I would get a payment and performance bond stating you have a fixed cost and over runs and unforeseen extra's are included in the contract. Not that this will fly...Things always happen.
Like the time I was doing a new roof. The client stopped the job because he wanted to have guest over for a couple of days. I told the client that I'm going to have to tarp over the room and I need an extra $250 to do that. The cost of a disposable heavy duty tarp and the labor to install it. The client singed a waver saying they stopped the project for 3 days, the time it would have taken me to complete the job and I wasn't responsible for any water, rain or weather damage. Then on Monday, the 4th day at 3:00am a rain storm came in. I had already talked with the home owners insurance and they agreed to cover any extra cost to protect the property if it did rain. The insurance paid me $250 and billed the home owners. Had there been no tarp, the damage to the drywall ceilings and floor would have exceeded $30,000.
I learned many lessons. If I have a cheap or stupid client , and that's around 50% of the people out there, then I will not take the job if they won't pay the price to cover known dangers.
Another job I needed parking for all of the tenants and my work team. Around 30 parking spots. There was a park around a block away. I convinced the Park Services to rent me 30 parking spaces for a month, until I got the job done. The owner refused to pay for tenant parking, they can find spots on the street. I paid the $3,000 for them to be happy and and have 24 hour parking . company.
--47.155.xx.xxx