You are both wrong. In order to charge someone tax for resale in a state, you need to have 'nexus'in that state. Live there, own property, have an employee that lives there. Otherwise, this is tax fraud. It's fine if you don't want to take my word for it. But before you commit tax fraud, I would do a free consultation with a tax accountant, which is one of my professions as well. I also have several friends that work for the IRS in the capacity of investigating and doing audits on small to mid-size businesses. I can guarantee you this is the law and what is enforced. I understand your point of view and I understand how it makes sense in your mind, but if you want to do it right, either obtain nexus in the state in which you plan to obtain tax, or charge tax for only where you have nexus.
There are many businesses that get away with this, and very publicly in ebay's case, but do you really want to take this risk?