My understanding is that if an online vendor has a physical presence in the state to which an item is being shipped, they are required to collect the sales tax for that state. I know that I pay WA sales tax when I order from Amazon, but many other vendors don't charge it, and I do pay attention, especially on larger dollar purchases. I always compare the TOTAL cost, cost of the item(s) plus shipping and sales tax to see which is the best deal. But then there are times when quality and customer service trump minor differences in total cost. Amazon is a VERY reliable place to buy. Usually.
