Hire a salesman, really? First, if you can even FIND a salesman that knows his a$$ from a swirl how do you intend to have him represent your company? To be able to sell the detailing business you need to KNOW the detailing business. That's not to say you have to be a master detailer, but you need to know what it is you are offering. You need to be able to educate the customer (on the spot) and respond to any questions and concerns they have.
If you're doing the work and someone else is the 'face' of your company that doesn't bode well for your position as it reflects to your customers. (You'll end up looking like hired help.) They'll drop off their cars, throw you the keys and expect to speak with your boss when they return.
Second, if there is indeed someone out there that can speak intelligently about the detailing business, chances are you'd be better off with that person actually DETAILING cars with you. Because, if you have the money to hire a salesperson, you'll have the business to put another pair of hands on the paint. Working WITH another person will get you farther than sending one out there trying to 'round up' business for you. Might as well hire a sign spinner for stuff like that.
Jus' thinkin' out loud.....