Keep the sales for sales reps and management, or decrease the amount of service calls to give more time for sales, and give the service techs the call in leads for the smaller stuff.
Keep the incentive pay at a reasonable and achievable level. when it gets to high and out of balance then it works in reverse, creating a lack of incentive, and discontent.
You're fooling yourself if you think that the super high selling techs still provide quality service at the same time.
Something has to give, balance between achievable sales goals, incentive pay, and route sizes/call counts is essential to reduce technician burn out.
Technician roll over effects customer loyalty, and retention.