Investments required to attract and retain customers are huge. Besides marketing, it takes big bucks to offer services such as a shopping adviser that makes recommendations for future purchases and gigabytes of editorial content geared toward the shopper's interests. Yet, services like there are precisely what help turn a first-time buyer into a habitual shopper. It is pretty clear that anybody can go online and sell things, but it takes a lot of work and significant resources to provide a customer experience. The Internet is a big, confusing place for a lot of people.
Customer service is very, very important.
If you give the customer what they want, they will stick with you. Bad shopping experiences can quickly deflate the strongest advertising efforts. That is not necessarily so. It's very complicated to build a smooth distributions system, deal with returns and handle drop shipments. The thing is that you can't expect customers to pay for all those expensive additions and improvements, at least for now.