Length: This is pretty self-explanatory. Generally the shorter the domain name, the more valuable it is. This difference in value decreases exponentially as the name gets longer, though. For instance, the difference in price between 3 and 4 letter domains are significant, while the price difference between a 7 and 8 letter domain would usually be much less significant.
The easiest way to see that is to go to HREFs and look at the anchor text. It reveals right away whether or not the site has been spammed. You also want to see if it’s been SEO’d too much. Right? In this case, it’s not because it has a brand name here and some natural keywords, but if the number one anchor text was like, cell phone management system and then the next one was like cheap cell phone management system, you’d know that the anchor text was manipulated and probably overly SEO’d. So, what you want as a site that has a natural link profile.
Wait for people to contact me: When I bought my two domains, I didn’t pay the extra $12 for Domain Privacy, learn about Domain Privacy here, so anyone can look up the owner of IHateCold(.com) and ReallyFunnyJoke(.com) in the ICANN WHOIS Database. It can tell you whoever owns any website unless that domain owner pays for domain privacy. So if someone was really interested in any of my websites, they could look me up and shoot me an email about their interest.
So how do you develop that instinct? NameBio maintains a database of over 500,000 historical domain sales (as of writing this post). They have interesting filtering features by which you can narrow down domains by price range, date sold, keywords and more. Simply sifting through the listings on NameBio long enough will quickly develop your domain appraisal “instinct”.