Hang in there Plankton,
There's something really satisfying although time-consuming and bloody hard, work converting dirty window frames from an old fashioned trad guy to look acceptable. As far as the employee, I think you've made the right call. No bad habit to correct, no know it all attitude to deal with and best of all you can train and hopefully mold him into the window cleaner you want him to be. Good luck pal, keep us posted.