There's no violation of any laws.Yes there is. For example, according to this reference provided by the State of Pennsylvania's Department of Revenue, "all states that impose sales tax also impose use tax," use tax being applicable to purchases of items or services that would be subject to sales tax in the purchaser's home state but for which sales tax is not collected by the seller. In many states purchases subject to use tax must be declared on the purchaser's state income tax return each year, and the use tax must be paid in conjunction with that return.
Regards,
-- Al