One of the first things you need to be a successful consultant is not only trust, but the knowldge that trust is a two way street. The client obviously has to trust you and be confident in your abilities and work ethic. However, to best way to design and present valid solutions to your client, is to have trust that they know at least a little bit about their particular business.
In the initial stages of requirement gathering and development, one needs to remain open minded and listen to what the client's issues are and what they are looking to accomplish. Trust them to know what the main issue is. Trust them to at least have an idea as to what they want their final solution to do. It's your job to sell them on how you think their goals can best be reached, not what you think their final goal should be. Help guide them if they need it, but make sure that your goals remain secondary to their goals. I would personally like to be able to propose to every client that they need a full integrated e-commerce solution for their website which keeps the store and website stock in sync as well as offers several ways for customers to contact and purchase from you. I also know from experience that not every client needs, let alone wants, something that complex.
On the other side of things though, the client needs to trust that you'll be able to complete the job. Obviously they trust you can do it otherwise you would not have won the job. However, for your own sanity and desire to complete the job on time (and hopefully under budget) you need to know that the client still trusts that you can do the job. Nothing degrades morale and the desire to work faster than someone either constantly checking up on your progress even though you've already given them an update as to where things stand. Trust me to get the job done and I'll get it done. Act like you don't trust me, and while I'll still get things done, I'll do everything I can to make you sweat until the very last minute grumbling to anyone who will listen the entire time.
It can be argued that the above is all based off of respect, which, as the idiom tells us, is earned. However, I believe that trust is a more basic concept than respect. You can work hard and do a good job on something regardless of if a client respects you or not (although chances are if they don't respect you to at least some extent, you'll never even land the job in the first place). As long as you take pride in your job, the respect isn't necessary, and will come in due time. Without the trust though, it makes it much more difficult to get the job done.
In the end, just remember to trust in yourself that you can get things done. Trust that your client knows what they want, and hope that the client trusts you.
