Governments often delegate regulatory enforcement to third-party firms that sell compliance services to regulated buyers. Competition in markets for these services may induce sellers to help buyers evade regulations, but may also lower compliance costs for honest buyers. I quantify this tradeoff in the Texas market for passenger vehicle emissions tests, where administrative data show that drivers purchased more than 9 million falsified tests from thousands of competing firms between 2002 and 2024. Entry of new firms raises the cheating rate at nearby incumbents by 6%. Each falsified test lets a driver skip repairs or replacement for a year, causing $27–$54 in health damages. Because prices are capped, competition benefits consumers through variety and proximity rather than lower markups. I measure these benefits by estimating an equilibrium model of the test market, including a spatial dynamic discrete choice model of demand for repairs and for falsified and fair tests at differentiated firms. A counterfactual monopolist cheats less often, but if it is allowed to reduce its per-capita locations to match monopolists in other U.S. states, drivers’ travel costs rise more than health damages fall. Targeted enforcement deters cheating at lower cost to drivers.

Dockless, shared e-bikes and scooters are a rapidly-growing segment of the local transportation market despite being taxed at higher rates per mile of travel than many conventional transportation modes, including motor vehicles. This paper asks what the optimal tax rate for shared bikes and scooters would be when accounting for environmental externalities and redistribution. We derive a sufficient-statistics model that describes how optimal tax rates depend on both extensive-margin (number of trips) and intensive-margin (duration of trips) demand responses to price changes, as well as the income of bike and scooter users and net externalities relative to other travel modes. We estimate the parameters of this model using trip-level data from Lime, a large bike and scooter company, and find that in several U.S. cities, use of their vehicles is concentrated among low-income individuals. The model accordingly suggests that policymakers in these cities might want to subsidize shared bike and scooter use substantially more than what can be justified by the  modest positive externalities it generates by displacing trips by motor vehicles.