Highly or moderately relevant. Is it conceivable that this website would naturally link to your money site? If you think it would conceivably naturally link to your site than it is moderately relevant. If there is no way it would link to your site unless completely randomly I do not consider it relevant.
Page Rank (higher is better) 0-3 typically n/a until update
Spam Check
Check anchor text for Porn, Pharmaceuticals, Poker or foreign language anchor text in Majestic SEO – If any signs of this kind of anchor text do not buy!
Natural Profile (no SEO) – Check backlinks for signs of blog network links, comment spam or directory spam – Use your discretion but if it looks like someone was doing low value SEO on the domain do not buy it!
Does the exact match anchor text look natural? Below 15% at least – If no Do Not Buy
Review website in Archive.org and see if the domain had content not related to the domain name – If the content does not make sense with the domain name it means it was already used as an expired domain (poorly used) – Do not buy it!
Redirection/Duplicate Check
Check if the site was last redirected to a new site by checking the most recent page in Archive.org to see if it was being redirected to a new site. If it was redirected before expiring then most of the juice seems to stay with the redirection. Do not buy.
Also check if all the old content has been moved to a new site – this may mean even though the redirection did not show up in Archive.org they did a 301 redirect on the old URL and Google has passed all the link juice to the new site. Use copyscape.com or this free alternative for this.
Registrar History
Check the registrar history if it has been registered and dropped multiple times you need to be confident it was not abused by checking it in Archive.org. You can check the number of times a site has been registered by visiting - http://whois.domaintools.com