If you really bought that gun and scope for 200.00, I would go there every day. Either they just couldn't move that gun, or they don't know what they're doing.

Make sure the barrel is free of lead. Some knuckleheads will shoot rifled slugs out of rifled barrels. Shoot the gun, see what it will do. My guess is that for your yardage requirements (75 yds) you will find satisfactory or better accuracy out of just about any of the sabot slugs out there. I would try a "fast" slug (2000 fps) a medium (1500 - 1600) and a slow slug (1300-1400) and se what your gun likes.