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Experienced domainers aren't the best negotiators. They have a value/price in mind for their domains and their minds aren't changed by the opinions of folks with little aftermarket knowledge or experience.
For a domain in your price range (offer 300 / demand 1800) my advice is to make your offer, put a time limit on it, explain that you are considering other options and move on if you don't receive a favorable reply.
[edited by: Webwork at 8:11 pm (utc) on June 11, 2008]