Cofounders don't get brought on to do sales. Employees do.
Treat him like a good salesman- give all kinds of incentive payments (commissions, bonuses) contingent on sales performance, but be very shy with the equity. Plan on firing him as a default unless he exceeds expectations quickly.
Equity corresponds to risk and skin in the game, and it sounds like he has contributed (and will contribute) very little to either.
Bonuses are paying him for what he accomplishes, equity is paying him for what you have accomplished. If he's any good, he'll make more from bonuses than even a 50/50 equity split. If he's not any good, then equity will be far more important to him, locking it in before performance is known.
And having just reread your comment, a salesman who doesn't want to do sales but wants to do management? You need to interview more sales candidates. HUGE red flag.
Have a beer with this guy and have a good time, but don't bring him on. The world is full of salespeople who can't sell and can't do anything else either. They get by through others' hope triumphing over experience.
Say, while you're giving away your equity for free, can I be your cofounder too?