I'm not sure exactly what you might look for - the lens is an excellent lens (I love mine and have no desire to "upgrade" in the near future).
I would say that looking for a lens like this used (as they're still not real cheap) - look at the front and rear elements for scuffs, scratches and the like, open the aperture all way (grab the little lever on the back of the lens and push it with your finger to open up the aperture so that you can look down into the lens at the light). You're looking for any fungus or mold... other than that, I'd say the lens is a great lens to buy used. They are either used to death (body shows many scratches, scrapes, scuffs, etc.), or used hardly and are in great shape (body shows little or no signs of wear). Make sure the tripod foot is included... and take your camera to shoot the lens. Make sure when you're focusing at the 200mm end, you can hear the VR working (that might be hard depending on where you are, but it's a little humming type sound). I'd say that most likely, the only thing that can go wrong with these lenses (or any AF-G type lens with VR)would be the VR.
My honest bet - you'll find an excellent one for the price you're willing to pay. I think there are more great ones out there, than bad ones...
I hope that helps someway (again, not really knowing what advice you were looking for). Good luck and enjoy the lens! You will... It's actually one of my favorite lenses to use! I've NEVER had any bad images when using this lens (and I use it maybe 35-40% of the time).
Check for cosmetic signs of abuse. Bring your camera with you. Mount the lens on it, and take the pair for a spin. Listen to the sound the AF makes. (It should be pretty quiet.) Check how the lens behaves when the limit switch is engaged. (Sometimes mine "hunts" for focus the first time it's used at a gig.)
This lens typically exhibits minor vignetting at maximum aperture at 200mm that many have noticed. (Nikon came out with this lens before their return to FX-sensor pro-D cameras. I don't think it's a problem: I see it, but I don't correct for it.) See how you feel about it.
I think it's a great lens. I use mine all the time. I bought it for use on my D2X's, but it's fine on my D4, too.
One more thing to look for is the condition of the lens foot. This is poorly constructed with a very thin plate where the lens foot actually attaches to the lens itself that can easily become bent and warped. At least one of the after-market companies makes a replacement that is much beefier.
All good advice so far, especially if you can handle the lens before purchase. But I feel the need to add what might be obvious - if you are buying sight unseen, be certain to look for a seller has a good track record, and a return policy you can live with if the lens does not appear to be as advertised. Finally, use a credit card if at all possible in case there is a dispute you cannot resolve with the seller.