Is shipping and handling taxable?
In most states it follows the goods: taxable order, taxable delivery charge. A minority of states leave a separately stated shipping charge out of the taxable amount, and several of those still tax a handling charge. The state that governs is the one the parcel is delivered in.
Does listing shipping separately keep it untaxed?
Only where the state says so. New York taxes a delivery charge on a taxable sale whether or not it appears on its own line. Massachusetts takes the opposite view and exempts a separately stated shipping charge, which means the same invoice can be right in one state and wrong in another.
Why is the word handling treated differently from shipping?
Because handling is work you performed rather than transportation you bought. California tells sellers plainly that handling is taxable and to use that word on the invoice when that is what they are charging for. Merging it into one shipping and handling line can pull the whole line into the taxable amount.
What happens when a box holds taxable and exempt items?
New York allows the delivery charge to be split in proportion to the taxable and nontaxable goods, and taxes the whole charge if the seller does not split it. Doing the arithmetic on the invoice is what keeps the exempt half exempt.
Can I charge more for shipping than the label cost?
You can, but padding has a tax consequence in some states. California applies tax to the whole delivery charge on a taxable sale when the seller keeps no record of the actual cost, and Massachusetts conditions its exemption on the charge being reasonable and reflecting real cost. Keep the carrier receipt.