First is a Realtor comes into your home and tells you they know the exact price your home will sell for, they are lying to you. If the price seems high and they do not have a clear reason for the price, tell them to pull out there check book and you accept the offer.
First things first. Look for all the homes that have sold in the last 6 months and as close of a proximity to your home as you can find. You need at least 4 homes that can be used as comparables to your property. These properties that you select should be within +/- 15% of the same sq. ft as yours and also with the same amenities as far as bedrooms, bathrooms, basements, lot size and year built.
From this point on determining the asking price for your home is as much of an art as it is a science. I also believe that you should price your home a little bit above what you believe the value of your home. The reason for this is buyers want to feel like they are getting a bargain and .by making the price a little higher you have room to lower your price.