For purchasing online there are several advantages as well as disadvantages of COD as a payment method
Advantages
1.low risk for the buyer, they pay only if / when the item is delivered.
2. The seller bears the risk, as some of the buyers may not be serious and may refuse to pay when the item is delivered.
Disadvantages
1. Difficult to track the transaction at a later date.
2. Some online stores charge an additional fee for COD , as courier companies charge a collection fee and this is passed on to the customers.
3. Many coupons / discounts are not available for COD transactions.