IT is not yet a mature industry, and there are few benchmark costs or standards to guide you when assessing a quote for work. Do you know how long it really takes to build a website? How much should you pay for a PHP coder or a business analyst? Do you really need 128-bit encryption on your email?
If IT is not your main business, there is no reason why you should know the answers to such questions. But accepting a quote without knowing the true parameters could cost you a lot more than necessary.
IT Intermediaries can slash excessive quotes to appropriate levels, at low cost to you.