How does the tradesman know how much to charge if s/he doesn't have a clue how much the job will cost, Fred?
Since you go on to say they don't want questions, do you mean that they don't want us to know how a quote is broken down in order that we don't question it? Aren't we entitled to know if we are getting the best possible value for money?
If you're saying that a tradesman quotes for a job without knowing how much the materials will cost, that's a bit worrying. I would expect them to know.
There isn't actually anything wrong with wanting to know what you are paying for materials and what for labour. Unless you know that, how can you know if you are being charged a fair price?
Actually, I tend to get them to quote, find out what they're telling me materials are and then say ok, that's fine, but don't worry about the materials, you tell me what you need and I'll provide them myself.
I find that by identifying the labour element first, as part of the overall price quoted, then removing the materials element by providing them myself - I actually save money. Even though they have access to trade discounts and everything.
I do the same with cars - how much for this job, how much of that is parts, how much is labour, that's great, I'll bring in my own parts, my brother in law works for an spares place, so I get a great discount.