Yes, I'm actually saying exactly that in:
> [a good contractor will] not give you answers right away, especially deadline and price. I can take several (sometimes billable) hours up to several days with a customer to understand the project and assess this.
I always include an escape clause in the contract in case they forgot to mention something very important that change drastically the price.
I also never quote the entire project, only the first deliverables. Then roll incrementally from that.
Most contractors around me are well paid, it's not a big deal to not be accurate at the begining. We adjust on the way.