I ran an Oswalt three auger for years.  The main thing is to not overfill them (they need mixing space in the back end of the box) and to rebuild the flighting when it gets thin.  Nothing will cause more trouble than ignoring a bent or weakened flight.  We ended up welding in reinforcing gussets on the bottom auger, since that's where most of the wear and damage occur.  If looking at a used mixer, I would avoid any that have the box itself worn thin or cracked through the bottom trough.  By the time that happens, the whole mixer is worn out and not worth rebuilding.