THAT HAPPENED in Washington state when I lived up there. The Indian Reservations could sell fireworks but you could not buy them off the Rez. I think it was in the city of Auburn, or near there (down below Seattle), where the Auburn cops would sit around in plain cars, watch people purchase fireworks, and then follow them off the Rez and have marked cars stop those cars and tell them they had been seen with illegal fireworks!!! They would then take the fireworks away from them, ticket them with a court date for illegal fireworks possession. I think I have the city right, but it was down in that area that they were doing that.
Here in Idaho, you can possess the fireworks legally, you just can’t use them.