>Isn't this at some level taxation without representation?
I'm not a fan of the ruling but I would expect the answer to your question would be: "No because you aren't forced to buy the product from a retailer in that state"
From the perspective of "the retailer is being taxed," then this _is_ taxation (of the retailer) without representation. But of course, almost every retailer passes sales taxes right along to the consumer, so "the retailer is beng taxed" is only true in a theoretical sense.
And if the retailer really doesn't like it, they can just not sell to customers in the state. But we know that's not going to happen. Like you said, the customer is the one paying the taxes, and the customer is the one who votes to elect those who make the tax laws that affect him.