Tropical, where the legality line gets crossed is when someone crosses the line that separates residents from non-residents. For example, many states require a vehicle that has come into their state to be licensed in the new state within 30 days. So the owner of the Montana LLC brings his RV into NY, for example, and leaves it here for more than 30 consecutive days. NY now comes knocking on his door and requests that he license the vehicle in NY. Now because the owners of the LLC are NY residents the state will require them to pay the difference between the sales tax they paid when they bought the rig to what NYS would have charged them. In this case, they paid no sales tax so they would owe the state the full amount plus penalties and interest if they were intentionally evading the sales tax. That's in a nutshell is how it works. Many an owner of a Montana LLC has had to pay their respective state a lot of sales tax, penalty and interest.