Is it true that you have to show up in a car with valid tags to be able to sell copper wire here? Or in the state of Washington?

No , at West Seattle, or at any place in king county or pierce. And u can drive into West Seattle. I go there all the time. Hope this helps

Pacific iron requires you come in a car west Seattle doesn't

The only thing you need is valid identification, as said above. And maybe also not have stolen stuff..haha

You have to have valid identification