Used MPB 16 bricked after seller remotely erased it
Apple covers exactly what to do to protect both sellers and buyers when exchanging hardware.

https://support.apple.com/en-us/HT201065

Often, only the original purchaser, with proof of purchase can get Apple to bypass an activation lock or firmware password.

https://support.apple.com/guide/findmy-mac/activation-lock-and-find-my-on-mac-fmm2dd428a48/mac
https://support.apple.com/en-us/HT204455