Do your due deligence and check on the market as best you can. I always provide a mini CMA for buyers to make sure they are getting the deal they aare looking for. Past performance will usually dictate future behavior, so pick a Realtor with a great reputation.
Bellasouth, Don't be concerned with your zestimate. It is a number generated by an algoritham that is probably a mile long. Most zestimates in King county, as reported by zillow.com, are off by 8.7%. You are more than likely paying for an appraisal, make sure it is done by a licensed appraiser using the standard practices for the industry.