[Stratoscope]

That's a really important point. To amplify on it, every ThinkPad has as many as three BIOS passwords: the hard drive password, the power on password, and the supervisor password. (Maybe even more than three, as individual hard drives/SSDs could have different passwords.)

The supervisor password is the one you care the most about.

You may get a seller who says "no BIOS password, boots up without a password." But the machine may still have a supervisor password, and if you don't have that you can't change the BIOS settings.

Always make sure there is no supervisor password, or the seller gives you the supervisor password.