Warning to non-profits. Do not take their phoned agreements as gospel. The rules may change when you appear as they did for us. Also a perfectly valid certificate of exemption will be refused unless it also contains your EIN. They do not warn you in advance. And your valid check may be refused by their draconian system and while they have an alternative method to verify it they may not use it. You may then have to use a personal credit card and pay tax. This can be reversed within 15 days. We were told 30 and missed the window.