For charitable organizations, the Colorado's Department of Revenue issues a "Certificate of Exemption" that authorizes it to purchase items and services used in the conduct of their regular charitable functions and activities without paying Colorado sales tax. This is sufficient documentation for the City of Aspen.
For governmental entities, some will have a Colorado issued tax exemption number, although they are not required to have one (tax exemption numbers begin with a "98"). In order for a governmental entity to take advantage of the tax exemption, the purchase must be made with a prescribed government form or purchase order, and paid directly by funds from the governmental entity. A credit card in the name of the exempt entity is acceptable. Some local governments issue credit cards in both the employee's name and agency's name. In many instances the bill is paid directly by the governmental entity and are tax exempt. It is not necessary for governmental entities to present a tax exemption number in order to make a tax exempt purchase.
A purchase by a governmental agent who is making the purchase out of personal funds, even if the employee presents a tax exemption number and plans to be reimbursed, is not tax exempt.
In cases where the seller invoices on a delayed basis for a purchase, the billing must be made directly to the governmental entity and not the person making the purchase.