our results suggest that uncollected sales taxes are much smaller than previously thought, and that they are growing, if at all, at a much slower rate. Indeed, two factors we have not yet mentioned suggest uncollected sales tax revenues are likely to fall over time, at least as a proportion of all taxes. First, there is some evidence that the online sales of the brick–and-click retail model are growing more rapidly than those of “pure play” purveyors such as Amazon.com.