have lots of parts on hand...LOTS. even boards. I have had a few stern sam's and my sys11's have many board issues and it is easy to just swap the board then fix the spare and have it on hand again.
Otherwise having flipper rebuild kits and swap balls every X plays or whatever.
Or have a spare game or two, that you can rotate out. If you don't have a large qty of games at the location, people get bored quick...ugh its annoying