One could argue Amazon's success is based largely on the unfair sales tax advantage it had over brick-and-mortar retailers. Brick-and-mortar retailers were compelled to pay sales tax under the penalty of law, while Amazon had a built in 6-9% since it didn't have to collect sales tax.

I'm not saying that's the only reason Amazon is successful, but it absolutely played a role. My early shopping with Amazon was always of two varieties - to purchase things I couldn't find elsewhere or to save money on more expensive purchases. Only relatively recently has Amazon become the most convenient way to shop.