Bookselling on the web is a complicated issue because it's worldwide. The answer you get will depend on the assumptions you make.
But in the context of the USA, it's a reasonable question since, as I think is inescapable, sales taxes are eventually going to apply to Internet sales. What would happen to Internet sales as opposed to local sales? If booksellers suddenly had to apply a $2 fee for book sales, I think it would be handled much the same way as all of the various taxes on phone service. There's a separate line item for them.
So, instead of $9.95 for your new favorite author's book from Amazon and free shipping, you'd pay $11.95 on the day that tax takes effect. Would Amazon feel they needed to eat the tax? Possibly not, unless they saw a drop in sales, or unless they felt they could get good press by absorbing the cost temporarily. But it's hard to know.
But, if you're like me, you don't look at your monthly phone bill and say, gee that local tax really burns me up. "You say, !%*##%! I'm going to cancel this if the price keeps going up!!!" It's the total cost that matters.
As Drew says, prices are usually based on supply and demand - not costs. http://www.thetrutha...iscounts-exposed/ Of course, in the long run, income (revenue) has to exceed costs, so there is a feedback loop in place. But Bill Customer doesn't care if it costs Amazon $12 to sell him a book if he can buy it for $10 from Powell's.
So how would it end up? It's hard to say. I think that in the long run the $2 would be added to customer's total cost. But, and it's a big but, if total sales revenue drops then companies will be forced to reduce their costs or become more efficient to make their customers see the value in making the purchase.
And in the real world, if it's only a US tax, then one could imagine that sales by Canadian and Mexican bookstores (or foreign affiliates of US bookstores) might see substantial increases.
Ultimately, the market will decide - not the booksellers. Assuming there isn't a cabal of booksellers, and assuming the tax is applied equally and can't be gamed....
So, the common view that "the corporation doesn't pay the tax, the customer does" is far too simplistic. It depends on a whole slew of factors.
My $0.02.
Cheers,
Scott.