They don’t have sales tax either. Every state with a sales tax has a use tax.
In the case of Delaware there is what is euphemistically called the "Gross Receipts Tax" which is an insidious tax that raises the price of everything, just not at the cash register, which is why it is called a "hidden" sales tax.
I recently spent a week there and just about everything I purchased there was by far more expensive than back here in Virginia. The only exception to that rule were certain items in places like Dollar General. But same brand/same store purchases are shockingly higher there than here. For example I purchased a pound of store brand butter in Food Lion the day before I headed to DE, it was $2.67 including VA sales tax. While there I needed to purchase butter, same Food Lion brand, same size and in "tax free" Delaware it was $3.20.