Hiring Your First Dedicated Salesperson: When Did You Make the Leap?

Following! I often think about this as I spend a lot of my time doing sales calls. I tried to have a "project manager" role that had a base salary and gross profit percentage as the performance pay. I discovered we needed a lot more jobs going at once to make that a financially feasible role. In my mind, a sales role needs to be keeping at least 3-5 crews busy and needs to be tied to profitability (not revenue) or there needs to be set amounts per thing they sell. 

I don't have a sales person though so one of you that does, fill us in!