Which gen is the KSG ? ( I assume this is the KSG. 12 rd. )
Some of the earlier ones had a few minor issues that can be easily taken care of, should yours need it. You may hear people tell you " Rack it like you hate it". That is utter nonsense and a good way to break a shotgun. Action wise it's an Ithaca 37 clone. All the action happens in the last 1/2", so you don't need to rack it hard, you just need to make sure you push and pull the entire length of travel.
I have a KSG25 ( gen 2) that has thousands of rounds through it with no major issues. The selector switch loosened up once which caused FTF. They should have used a shoulder screw. You can't tighten it all the way or the switch don't move. The solution ( should you have this issue) is to degrease the screw and the threaded hole, put a little blue loctite on the screw then tighten it down and then back it off until the switch moves. Then let it sit for 24 hours to set up.
Anyway, nice score. I paid $800 for the KSG25 new several years ago. You can't find them for less than $1200 last time I looked.