I'm a newb when it comes to this, but out of curiosity, what do you look for appraising a domain name?
Keyword saturation, how many searches do the keywords get, whether the name is brandable or not, hyphens or not, extension domain is using etc.
I'll piggyback on danger's points... There's SEO factors and human factors. SEO: keyword saturation and search volume of that and related searches, if you're buying it from someone then domain age, Pagerank, etc. Human factors: brandable domain, hyphens and non-dot-com extensions lead to distrust if you're trying to sell something. Also in terms of human and SEO factors, it's better to have the most core meaning of a word and pick up related keywords rather than missing that core meaning... what I mean here is the domain "bookstore.com" will pick up "novel" and "textbook" related searches, but "novelstore.com" is really only likely to pull in people searching novels.