I'd check with both your accountant, AND the contractors' board as to how this relationship should be set up.
For example, if they are selling the job, then hiring you to do the work, this puts them in the position of being a general contractor ... for which they need to be licensed.
Or, conversely, suppose the salesman gets in a wreck ... are you on the hook for the workman's comp claim of your "agent?"
Maybe there's a legal way to do this, but you need to CYA.
