You can set a target-based incentive. This can be at different stages.
Tell them that if they complete 15-20 outlets in a month (the number depends on you), they would receive a fixed amount, which you have to decide. Then for 20-30 outlets, a fixed amount, for 30-50 outlets, another fixed amount, and above 50 outlets, a fixed amount.
Alternatively, you can also inform them that in a month, they must complete a fixed 20 outlets (again, depending on you), and for each outlet above that, they will receive a set amount (e.g., Rs 200/- per outlet above 20).
I hope this helps you out.