The rack gears come out of the rack- if anything is seriously wrong (like it's full of water and rusty, etc) you'll catch that.
What you want to see is relatively clean (hopefully, greased) gear teeth with little wear, and no ugly wear or galling on the side opposite the teeth that slides against the 'pretensioner'
Beyond that, if it feels good, it's probably good. They really don't go bad very often if the boots are intact.
hth, and good luck,
"I'm sorry. I actually had to poop and ended up breaking the car."
- Hot Tub