do u know how to use your friend's account?

i think same before, sad, but steam dont protect your account absolutely

You beat me to it by 1 minute xD

Can you still do things with those accounts like accept offers or is it just for games, like family sharing?

do u think its safe and is it normal steam politics?

It does ask for password, if you uncheck "remember be" tickbox when logging in.

Source: I have a SteamOS machine that boots into big picture mode with three accounts, my kids just log in and play the games in family view, while mine is password-protected.

Unless maybe it works differently on Windows, though I'm not sure why it would.

Are you sure about need to exit? On Linux, if I want to switch accounts I just go into BPM, log off the current user and select another.

do you think its correct?

imagine your little kid log in to your account and use cheats (kids dont understand difference of fairplay and cheating) and u ll get VAC

or one of your friends want to trick with u - they will bue game and send to himselves

this will be not happy

people often do this when want to sell some rare ingame stuff for real money

Exactly. This sounds more like a problem for people abusing the family sharing or poorly implemented cyber cafes.