I am of a different opinion.. I set a price.. If the buyer says NO WAY.. then you walk away. If the buyer is a possible whale.. they will counteroffer even though the counter may be for 10% of the set price.. you have their attention. At that point, I simply state the benefits of owning a premium domain name, and say something like "The domain is priced at a fair level, I am not going to waste your time countering back and forward. If you are interested in the domain then I would need to see an offer that we can work on, otherwise I will have to wish you all the best and withdraw myself from these negotiations."
Most will walk away at this point, however around 60% will come back and try to haggle you some more.. at a more agreeable level.
I have 2 domains out there at the moment, that I have been negotiating on for around 2 months now.. and they always keep coming back. One domain deal I done earlier this year was a £45k 3 letter .co.uk domain, the buyers refused to pay the £55k.. but agreed to lease the domain on a 4 year contract at £1000 a month, with the option to buy at the set price by given us 6 months notice. So do the maths on that one.. 4 years at £12k a year plus the £45k... of course they can walk away after 4 years owing nothing.. but I will still own the domain and will have earned more than I could ever have sold it for.
I also have around 25 domains all leased out on annual contracts for around $30 a month each.. dont let a deal go, make it worth their while.. and show that you are willing to deal.. every offer is a potential customer... treat each offer with respect and dont let the buyer sell you.