Well, I for one don't need the panic call while I'm in the middle of another job 50 miles away because some twit tried to change something and something no longer works.

This is why we don't allow customers tech level programming access. If they insist on manuals I SELL them new at FULL mark-up. I also make a back-up of the system, this way I have a record of what I programmed. We also inform them of a $200 "restore" fee.