To avoid requiring every person who happened to sell an item of tangible personal property during the year to collect or pay sales tax, most states offer an exemption from sales tax for occasional, casual, or isolated sales. In most cases, eligibility for the exemption is based on the seller not having more than a specified number or dollar amount of sales during the year. Among the states having a sales tax, Colorado, Oklahoma and Wyoming are the only states that do not provide specific exemptions for occasional sales (with the exception of occasional sales by charitable organizations).
However, a number of states deny the exemption to any person who is normally
engaged in the business of making taxable retail sales. In contrast, other
states allow the exemption to retailers with respect to sales that are not made
in the regular course of their business.