ergophobe - 8:33 pm on Feb 8, 2011 (gmt 0)
Like everyone says - if you had an agreement, end of story. I can think of a zillion cases in my life where I've benefited and paid dearly for such agreements. You know going in that if you ask for a fixed bid, a smart contractor is padding his bid to cover screwups in the estimate.
The key here, though, is whether the original contract was a fixed bid or an estimate based on projected manhours.
I have never had a mechanic, general contractor, plumber, electrician, tree cutter or any other respectable tradesman try to weasel out of a fixed bid contract. I've had some look like they wish they could, but they've never even asked. Recently, a mechanic gave me a price based on 4 hrs labor. He ended up taking over 10. No price change. But he knows that I send everyone to him, I've bought six sets of tires there and more and more. He's getting it out of me on the back end.
I have also had some *refuse* to give me a fixed bid because they felt there were too many unknowns and basically just said "you'll have to trust me on this" which I did, with excellent results (after checking references or, in some situations, after having done business with them already).
But trying to triple a fixed bid partway through the process? I'd see a lawyer.