Take off the intake pipe (where ambient air is fed into the turbo) and spin the wheel. It should spin pretty freely without any rough feeling. Sorta hard to explain
Also check for excessive side to side (lateral) movement. Basically, if you can feel or really hear the bearings, it's time for a rebuild. You can't realy tell anything by just looking at it, unless it's so damaged that the damage is visible (which would be very bad). What kind of car is it and how many miles are on it?
'98 Super Black SE w/stuff