How to remove iCloud activation lock from iPhone

I bought an iPhone online and it has an iCloud activation lock. I tried to contact the seller but poof they are gone. I’d like to find the original owner as maybe this was a mistake or maybe I bought a phone someone lost or worse it might be stolen…the phone is wiped clean and starts up normally for new set up only to eventually hit the iCloud lock. I don’t want to invest a lot of time into this, what’s the simplest way to resolve this?

[Re-Titled by Moderator]