yes, it's correct. it's state sales tax. If you are physically in the state buying an item you will get charged the state tax. If you are out of state buying an item from a different state you are not subject to their sales tax.
Yes. The purchase has to be made in one state and delivered to another that does not have a store in that state. Adorama has no store in Tennessee, so they don't collect the tax for Tennessee. Some states want you to claim the sales tax and pay it at the end of the year, but few do.
It doesn't stop there.. If in another state in the US, we can use the same method of buying online and not paying sales tax. However, we are then to pay a "use tax" to our home state. No one knows, or pays attention to this until they are audited.