There are two main ways to establish a home listing price:

1) Get a full blown appraisal: A certified home appraiser will give you an estimated market price for about $300.

2) Get a "CMA" (Compartive Market Analysis): A CMA can be provided by a real estate agent. The agent will look at recent sale "comparables" and determine the market price for your home. A comparable is a house similar in size, age and condition that is physically located near your home and has sold recently. Comparable sales are the best indicator for what your house could sell for. (And actually, this is pretty much exactly what a certified appraiser will also do.) The advantage of a CMA over an appraisal is cost--A CMA is free.

Ultimately the market decides what your home is worth. The true definition of "market price" is what an able and ready buyer is willing to pay.