[vgalin]

This 'someone' could also, on most computers, install a keylogger to get your master password, or passwords that aren't registered in a password manager. Would you consider this a vulnerability coming from the password manager?

[that_guy_iain]

In most cases they wouldn't be able to do that. Because there are security measures to prevent that.

[blincoln]

What security measures do you think would protect against someone installing a keylogger or extracting saved passwords from your browser data files if you let them use your computer?

Also, are you envisioning setting up a new, non-administrative user account for that person, or just logging on using your own account and then handing over the keyboard and mouse like most people would do?