Hope this helps, -George
From some/little experience in both buying and selling a couple of domains. I would make the offer known to the seller and then back away. If they are going to sell it they should contact you within a period of time. This has happened to me in the past I made the offer and walked away, a few weeks later they contacted me with a price nearer to my initial offer, I still insisted on paying $500 they eventually gave way and I secured the domain.
Hope this helps,