Recently, I've had similar conversations with a few brides when discussing their wedding vendor selection process. They mentioned their disappointment that the planner/photographer/florist/etc. they were initially interested in booking, ended up getting booked from under their noses. Word to the wise: don't wait too long between initial inquiry, setting up a face-to-face, and then making your decision. In my opinion, a "reasonable" amount of time is 3 - 4 weeks from first contact to final decision. Most vendors will NOT"hold" your date without a signed contract and retainer, although some will give you a polite heads-up if they get another inquiry for your date... and many will not! Personally, if I have met with a bride for a certain date, I will hold their date for about a week and also offer them "first right of refusal" if I receive another inquiry for the same date.
Another note: if for example, you have 4 more meetings scheduled with other planners/photographers/etc. over the course of the next few weeks (true story), let them know! But then don't be surprised if and when that initial vendor gets booked... the early bird gets the worm :)