when i prchased my used warn 9000i, i looked at three things;
#1 dose it have power in and out?
#2 dose the lever ingauge and disengauge easy or hard ?
#3 overall looks
If somebody wants to sell it bad enough they will show you that it runs. if they donot then buyer beware.
If the lever turns with out to much force , you should be good to go.IFyou have to use to much force or it dose not move at all , it needs some work inside.
If it is all rusted and beat up it might not be worth the time and money to fix up.
I am shure there are other things to look for , but this helped me to get a good used winch.