To gain your clients trust you must do this: "TRY EVERYTHING". With in reason of course you don't want the client saying "let's go through all of your sounds" when you have 2TB of samples and every synth known to man in your arsenal. What I mean is try your clients ideas so they know why they do or don't work. As producers we can tell when something will or won't work. To set the client at ease just say "Ok lets try that". This way you gain their trust and they can rest assured that you know what you are doing and that "YOU STILL HAVE IT".
I had clients say "Cori I'm going to shut up now and let you do your thing". The best answer to this is: :)
Trust is everything. Without it no amount of money is worth not being trusted. Believe me I've ended projects because of lack of trust.
I've heard of some producers playing games with potential clients. Just playing basketball, checkers, hanging out. Some clients say "Why are we just hanging out? We are suppose to be working". The producers would reply "We are working." Before you go balls deep into production a good producer has to know what he/she is dealing with mentally in the client. No one wants to work with a "High Strung" control freak that is bi-polar.
So to weed out this type of person, even though they have thousands to spend on production, you just need to spend a little bit of time getting to know your client. If you are happy then you can produce something that makes the client happy.