Buying a Used Macbook, iCloud I'm purchasing a used 2013 Macbook Air on craigslist and the seller told me he formatted it already and created a dummy account so I can go through settings, etc.. and browse around to ensure all is working.

I want to be sure that I do not get locked out of the Macbook Air. If he formatted and logged out of iCloud, what is the best way to check that I will come out of this purchase safely? Should I log myself into iCloud and turn on 'Find My Mac'? 

The reason is it is an old OSX so I need to do some updating afterwards. I don't have experience buying used macbooks so any help is appreciated, thank you.
Mac do not have hardware activation lock. Read the last paragraph of the "FAQ" for confirmation.


https://support.apple.com/en-us/HT201365


You would want to check for a Firmware Password which might need another question if you don't know what that is, but iCloud cannot prevent you from reinstalling an OS or activating any Mac that has shipped thus far.


https://support.apple.com/en-us/HT204455


Since a bad actor could use the lock function to remotely set a Firmware Password, your step of logging in and signing into your iCloud and successfully activating Find My Mac and locking it would ensure you have exclusive control of that device going forward.