The de jure minimium age to purchase tobacco is 21 now in the US, so I guess anyone see to sell tobacco products to those under that age could be held responsible as well.
They are held responsible by paying a fine to the government or losing their tobacco license, which is better than nothing, but doesn't actually fix the harm they caused already for the kid that's now hooked.
They are held responsible by paying a fine to the government or losing their tobacco license, which is better than nothing, but doesn't actually fix the harm they caused already for the kid that's now hooked.