if all this person is going to do is sales than commission is the best way. the more they produce, the more they make. a commssioned sales person can never get paid too much. of think about a draw against commssion. this works as sort of an advance against commission. also they may want to annualize their commissions so they get a check all year.
I say scrap the idea for a sales person. That is a non-value added position. Hire a good forman in do the sales work yourself. Already have a good employee that could take control of the crew??? That is even better. Add another laborer and you have added production at the lowest possible cost. You SHOULD be the best salesman for your own business. Who better to go meet that potential client than yourself. In the lawncare biz it is hard to retain clients that are willing to shop unless you provide some sort of trust. If they know they can deal with you and get things done, they will be more likely to stay.