A certified appraiser analyses past sales, computes the cost to reproduce a structure and determines the worth of future income that a property might produce.  A good appraiser will also be able to explain to you all the approaches used to estimate real property value.  Please note that when a real estate broker perform a comparative market analysis, the resulting opinion of value may not be referred to or constued as an appraisal.  

In order to reduce the possibility of any conflict of interest appraisers are paid a fee, not a commission.  The cost of a appraisal vary depending on the difficulty, time and expenses involved in the appraisal process (usually around $150-$400 for an ordinary home).  A certified appraisal may help you not only price your home right, but also convince buyers that your home is worth what you are asking. 

If you intend to place your own estimate of value on property,  you may want to gather as much information as possible in order to make an informed decision.  For example;

You may want to;

-Review recent sales of "comparable" properties (in the same market area) similar to your "subject" property

-Compare those "comparable" properties with your "subject" property

-Take into account; size, age, condition, location, additional features, price per square foot, market condition, time of sale, replacement cost, motivation, and other factors…

-Recognize the differences between your "subject" property and each other "comparable" property

-Make necessary adjustments to make the "comparable" as similar to the "subject" as possible

-Know the difference between market value, price, and cost

-Understand the factors that determine value

-Seek the opinion/advice of a professional.

Even if you've decided to place your own estimate of value on the property, you should consider talking to a professional in order to double check your findings.   Many agents and appraisers will tell you (for free) if your home is underpriced or overpriced.