Years ago I gambled and bought a highly used Nikkor 70-200 f2.8 from either B&H or Adorama (forgot). When I spoke to someone at the shop I was told straight up that it looked like it had been to war, but the glass was pristine (upon delivery the description was accurate). After a couple of years and thousands of pictures, the auto-focus started "squealing", although it would still focus. I sent it to Nikon service and they ended up replacing the entire focus mechanism and the "bayonet" portion of the lens, which had a small chip in it (but did not affect the lens' ability to hook up to the camera body). After all was said and done, I had my lens back in about 3 weeks or less, and spent about $550 ($475 service and parts, plus shipping both ways, and taxes). In the final analyses I still ended up paying a couple hundred less than full retail value (or about the cost of good used lenses) and had a brand new focus system (includes the VR system). As of today I estimate I've taken another 10,000 pictures with it and have had no issues
If the lens is not under warranty, they will send (email) a quote and require your concurrence to go forward with the repairs. If you do not want to continue with repairs they'll send you your lens back (but you'll have to pay the return shipping).
Good luck to ya'