If you have your own ladders and van, insurance etc, you may just as well go round looking for grass growing out of gutters. Buy a squeegee, bucket and applicator and clean a few windows while your at it.
Paying a guy just 15% when he's using his own equipment is a joke.
I would let him keep 60% for cleaning windows, and if he can do 10 gutter jobs a day he would have no problem doing 40 houses on his own.