There are advantages and disadvantages for both the seller and buyer in online commerce.

Seller
Advantages for the seller include:

Access to worldwide markets
Minimal sales costs
Can compete with larger companies
Can track purchases and use data to recommend other items to the customer
Disadvantages to the seller include:

No personal contact
Expense of getting popular—servers, etc.
Must get people to know about and visit the site
Buyer
Advantages for the buyer include:

Can find hard-to-get items from his or her chair
Reduced cost
Automated cost-comparison available
Disadvantages for the buyer include:

Must pay for shipping and wait for delivery
Cannot see or feel the product before making a decision
Cannot easily return item or get support