What dismayed and amused me about the firms I had quotes from for my mother's flat, was the speedy way in which the original estimates came down in the face of my intransigeance, to a third of the original in one case. I "innocently" asked how long the job would take and how many men. These questions were innocently answered. That gave me a base cost for labour. The rest was material cost and profit including the salesman's commission. The cost of material won't change, so the variation is in commission and othe profitIt's fairly easy to find a rough idea of material costs, before or after any quote. Then you say for each reduced quote that you're surprised at the man cutting his labour rates so much; you'd hate to work like that for his firm ! You can propose your estimate and see how close you can get the price. The salesman will "make a call to his manager", several times, and report that he's just been told they have a special offer, then that "just for you" his manager has reduced the quote, and so on. Eventually you'll get somewhere near right.