Some characteristics of valuable domain names include:
Length: 3-4 letter domain names are inherently valuable because it is impossible to register more of these domain names (they’re taken), and many of these domain names can serve as exact matches for brands or companies.
Age and Authority: Aged domains typically have greater domain authority due to their age and the potential they’ve had for gaining backlinks over the years. This is another reason why short domain names (that were probably registered 10+ years ago) are so expensive.
Brand-Ability: Qzjc.com or some random 4 letter combination isn’t the easiest domain to transform into a brand…privatejet.com or aaa.com on the other hand have potential and are very straightforward.
Domain Extension: .com domains are the most valuable domains around, but .org, .net, and some newer extensions like .io are still capable of putting up some impressive valuations.