It's a beautiful day, and you go house-hunting with your real estate agent. He/she shows you a number of houses. Some are just okay, but there are some houses that you really don't like. Instead of telling your agent what you don't like about some of the houses you just saw, you just don't say anything.
When you go into a house and you don't like the style, for example, you really should voice your opinion, whether it's asked of you or not, or your agent will show you that style again and again, not realizing that you don't care for it. Your realtor doesn't (or shouldn't) take the rejection of these houses personally.
Not being vocal doesn't help you or your agent in the long run. What you don't like about a house is just as important to know as what you DO like and want in a home. It is important that you tell your agent the good and the bad about each house, so he/she can tailor your home criteria accordingly. Write it down on the MLS property sheet at the end of each showing, if you need to, and discuss it on the way to the next house. Don't wait until the end of the day- each house's features can become a blur.
As always in real estate, communication is Key.