At some point the tape removes itself!
He just had cables. You can slide a new one in there. With the Jagwire Sealed lines, you can just change the liner.
I own a bike shop & have had 2 customers come in with snapped bars due to this problem, Fit new tape every 12 months & check for damage!!!
Sell those people some gloves! 
Maybe their bars need to be sprayed in some kind of epoxy paint!