The fee starts at 6% for sellers, people selling twenty dollar bills for bitcoins. As they make more transactions it goes down to 1% on their 10th successful transaction. This is meant to reward honest trading and avoid having an initial charge for a seller account.

Comparable services usually have a initial charge to sell, and SR recently raised their fee to 10% fee.

Buyers have 0% fee since we cannot realistically issue a fee to buyers.