Ecommerce is a good source of Bitcoins, but only few people will have access to this earnings possibilities. It's not possible to everyone to be the employer, the boss, most people will be the employees, they will work for someone. In this case, the product or service owner will hire some people to sell his products, to work for him.
I think people shouldn't look only for the best source of Bitcoins, but try to find many opportunities to earn more in different forms, this way, people can increase their income even not using the best source.