First off, are you sure the trigger is broken or is it just gummed up. Since the guy obviously was lacking in his cleaning and care for the rifle then it could be the old Triple 7 effect on the trigger grouping. Clean the barrel with a good cleaner then hit it 50 or 100 strokes with some JB and check for pitting. It could just be surface rust inside the barrel. Clean it all up and then check it out. Could be a diamond in the rough or it could be just plain old rough.