I bought a lens like that my 70-200 off a forum. I have included a pic of my scratch. I immediately had some buyers remorse after buying it b/c I was pretty new to the game and was afraid I got ripped off, even though articles and everyone said it'd be fine. Turns out it was fine. I saved $, got a good (yet old) lens. I continue to use it and will do so till it croaks, then I will buy a brand new one.
Check out my smugmug:
All my wrestling and jiu jitsu pics under "sports" (except the RMNU camp)
Under "nature" check "butterflies in flight" and "hummingbirds"
under "people" check "brett dione dallas"
All those pictures were taken with my "scratched" lens.
Here is a picture of the lens itself. The "scratch" is 8mm and theres a few smaller ones that didnt show up in that pic. If you can get a good deal on this lens, I would recommend it as it's a good savings, esp if you are just getting started.
Have the seller send you pics at various apertures as well as a sunflare pic.