Like Guerilla clearly said why take on so much risk? It's pretty fucking scary the amount of people around here who lack the basic concept of risk management.
I think doing some research before hand to determine demand would mitigate a lot of risk. Having only 3 or 5 scooters on hand to rent out if more than 1 group of people wants to rent scooters is just leaving cash on the table. What if a group of 6 guys comes along and wants to rent scooters for the day and you only have 5 to rent? You're not going to rent any then.
Having 10 of 15 scooters rented out for the day is far better than having none of 5 rented.