Its a fact that there are many disreputable agents out there. Yes, there are many agents out there who are only out to make their commission and will thus do whatever they can to make you pay more for the house.
On the other hand, there are many agents who understand that they're in it for the long haul, that they want your business when you decide to move again, that they want your friends' business when you have a good experience with them and recommend them to others. If a reputable agent thinks the house is overpriced, they'll tell you. If a reputable agent thinks a house isn't right for you, they'll tell you.
There are all kinds of ways to find a reputable agent who will deal with you honestly and help you find the house you want at a reasonable price. Ask your friends for recommendations. Ask the agent for references to recent buyers, and talk to the buyers about their experiences. Ask the agent how long he/she has been in the business and how long he/she expects to be in the business. Check with local licensing and consumer-advocate groups to see if there have been any complaints lodged against the agent or his/her firm. Google the Web and News sources for the name of the agent and his/her firm to see if they've shown up in the news in a bad way.