Look at what you get when you are paying a 20% commission on gross profit: you pocket $4,000 for every $5,000 of gross profit your salesman generates. Sure, a great salesperson will make a killing with this type of pay plan, but you're going to make an even greater killing. You want your salesperson earning $200,000 because that means he's contributing $800,000 to your OH&P. Imagine having four such salesmen in your firm. How well-off would you be?
This type of pay plan will draw top salespeople to your company. Where else in the construction industry, or any industry, are they going to have a chance to make that kind of money?