How to check a boo mac?

Question

macOS

Good afternoon, I'm going to buy a boom mac from my hands, I read articles on how to check and chaos with a key pressed and check the battery charge cycle, but there are two nuances for which I cannot find answers.
1. On one site, it was advised not to take a mac with a firmware password under any pretext. Why? Is it really impossible to reset this password if the owner knows it. Or do not discard, but simply write it down on a piece of paper?
2. How to untie the owner's apple id and bind your own? I read that after unbinding, the new owner received notifications about what the old one was doing.
And in general, how to protect yourself from the fact that the old owner has no more access?

Answer 1

1. I didn’t quite understand what it was about, but it’s better to reset all passwords, because, again, if I don’t confuse it, then perhaps here we are talking about the fact that Apple devices can be remotely blocked. It’s quite difficult to pick up such a password, my colleague was “taken away” in this way the device, he spent one week unlocking it (the device on Aidurin sorted out the password to turn on the device all week).
2. register your AppleID and, at the time of the transaction, link the poppy book to your account, before transferring the money, right in front of the owner. You need to do this through the settings, as well as in iTunes.