graeme_p - 8:00 am on Jul 27, 2012 (gmt 0)
You are selling the domain but keeping the site?
It depends. Domain prices seem quite unpredictable. There are some general rules such as a premium on common words and short domain names (especially short dot com ones).
The buyer says "There's nothing on the domain, however. The indexed pages in google don't resolve".
Is that correct? What are your traffic sources? Can any easily be redirected to the new site? Will the new owner of your old site do something to inform visitors (perhaps including bots) of where your new site is?
What people pay for a website or a domain varies a LOT. I have got offers varying by a factor of 6 times between highest and lowest for the same site at the same time - and I have not got a bid from the buyer I think is likely to pay the most, nor have I contacted every possible buyer I can reach yet.