In order to set your minimum and maximum quantity in a product in the inventory module, follow theses steps: 
  • From the POS, click on the "Spy glass" to access the inventory,
  • In the inventory, select a product,
  • Add the minimum and maximum quantity, 
  • Click "Save".

You should only stock more then one item for vehicle that belong to customer that comes more then 2 times a year. 

Keep in mind that the inventory in money you don't have in your bank account. Inventory item should turn 3 to 7 times a year,