When I was working construction, our sales people earned commissions of 10% up to 20% for our most senior sales guy. He was the only one who made more than 15%. The majority were around 10% to 12%. And they had to earn an increase in their percentage based on performance. It took a while to get an increase. Trey hit the hot button. You have make sure your margins will allow for the commissions, otherwise you're in trouble.
I can't wait till my company grows to the point where I am looking for sales people. Right now it's just me and my wife. My daughters help out on occasion. But not that busy - YET.
GOOD LUCK!!