Ray, if there is no tax on the vendor when they buy from the manufacturer then I cannot see how there is a double tax.
I'm still not sure that you have that correct but I'll give you the benefit of the doubt since you are trained, at least somewhat, in this area.
I will tell you that waiting for years before you go after this type of tax is, in my view, not ethical, or right, no matter how legal it is.
I'm also not quite sure that it's ethical, or right, to charge a home state tax on something that is bought out of state, whether you bring it back to your home state, or whether it's delivered to your home state address from out of state.