Only registered businesses can charge and collect taxes on goods and services made in Taiwan. As auction sites are places where individuals can conduct business activities for profit without paying business taxes, Taiwan’s tax authority has ruled that profit-seeking individuals must register as businesses and pay taxes. However, the anonymity of sellers on Internet auction platforms poses challenges to the ability of the tax authority to enforce this ruling. This paper examines business tax policy for online auctions in Taiwan and then assesses the prospects of taxing sales on online auctions using a game theory model. Analytical results suggest that seller anonymity will allow a vendor to continue to disguise business identity and the tax authority will not aggressively pursue tax evaders.