I am with Don, I would think about hireing a foreman who can go to the repairs and oversee jobs for you before a salesman might be a better bet. If you look at paying yourself commission on every job vs. Paying it to someone else it’s more profitable for you to do it yourself.
If you are doing the sales you are also control what jobs you are selling. Sales guys are good at one thing, selling jobs. It all comes down to money, when a sales guy is slow they are liable to sell low or less desirable jobs just to get a paycheck, cutting into your profits. In my experience When sales are good and they have plenty of leads, they chace the new business and neglect overseeing the jobs currently in progress that they already got paid for.
Just my experience but most sales guys are horrible project managers, espically overseeing subs. It takes a good roofer to be able to pick up on shoddy work, corner cutting, and identifying future problems.