How valuable are four letter domains?

[DannyN]

hello domainers, i'm wondering how valuable are four letter domain names without any numbers or hyphens but not actual words for example zxza.com?
ty

 

[JoshHendo]

I am sure I have seen another thread like this recently. well, anyway, in my opinion, 4 letters will never become valuable (unless it is a common word etc.) because there is a bigger combonation than 3 letters

 

[monRa]

No much value, I have bought once years ago but selled for less!