First thing is the bluing and wood (older was before plastic ). Nice even wear isn't necessarily bad, but rust and or gouges are red flags to me. If they didn't take care of the outside I bet they didn't take care of the inside.
When you take it apart, look for wear on the metal. The magazine tube, the action bars, the link, where the locking lug engages the recess in the barrel. Sometimes you can tell more by running your fingers over it than by just looking. If the surface is noticeably lower than the adjacent metal, it has likely see quite a few rounds. Check how snug the barrel fits, and how much play there is due to wear in the receiver slots. Don't go by the sharp edges because those can be there after 100 rounds. Take the trigger group and move the carrier and look for wear, and cock the hammer if it isn't, and drop it with the trigger, catching it with your thumb, looking for excessive play. Anything other than the receiver and magazine tube is a drop in replacement, but at a price, so put the adding machine in your head to work.
The only 1100s I have ever seen with really noticable wear were skeet or trap guns. Some of them have seen hundreds of thousands of rounds. Haven't seen that many sporting guns for sale. I bought an old 28 gauge field gun that had been set up for, and used for, Skeet and Sporting; a lot of Skeet. The blue was a little thin, and the action bars were really worn, the link had a little wear, but everything else was great, and the wood was "new" because they had put checkered Sporting wood on it to shoot it. I replaced the action bars and link and have had no problems. She locks up tight and runs like a typewriter.
