What are the factors that determine what your website is worth?

Things to consider when selling a domain:

#1 Most Important - Supply and Demand

#2 Is your Domain parked? or are you selling a  Domain + a Website?

#3 Factors - Webstats and SERP Rank -
How well is your website working in the search engines such as Google, Yahoo and Bing and Alexa.

Using a mathematical calculation these factors could be factored in to your website value:

Alexa Rank:  Quantcast Rank:  Compete Rank:  PageRank:  Backlinks: Google Indexed Pages:   Google Indexed Images: 
Yahoo Indexed Pages:  Live Indexed Pages:  Dmoz Listing:   Dmoz Title:  Dmoz Description:  Dmoz Category:
Host IP:  Site Hosted in: Owner:  ICANN Registrar:  Site Age:  Created:  Expires: Updated:  Domain Suffix:

Find a Website/Domain Value Calculator using "What is my Website Worth?"
(We don't have a calculator here because the calculation is only a number based on the above items).
 

Custom Search Based On A Customized List

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The bottom line is that your buyer can just as easily use a different domain name and add pay per click to outrank your domain.
The domain you are selling may "feel" priceless to you, but asking too much for your domain is like shooting bean bag bullets at your potential  buyers!