Bicycle Mechanics - how can i tell if a disassembled headset is pitted or otherwise messed up

thanks

After cleaning them, look at the bearing races. If you don't see pitting, it's not pitted.

When the Headset is fully dissassembled, put it back together by hand. With no pressure, but your hands force on it. Turn, and see if it is bumpy or smooth. Sometimes its not as easy as looking at it. The eye cannot see everything-

Look at it with a magnifying glass.

Lightly run a ball-point pen around the bearing race, right where the bearings make contact. It should feel smooth all the way around.

The races most likely to be damaged are the bottom ones, the lower cup in the headtube and the "crown race" (the race pressed onto the fork steerer tube). Pitting and pock-marking of these races are pretty apparent if you inspect them and are cause to replace the headset.

The upper cup and race are rarely damaged unless they get full of water or something similar happens.

+1 on the pen. I've yet to meet a headset that I couldn't get to a satisfactory condition simply by replacing bearings and repacking.