I connect commodification arguments to an empirical literature, present a mechanism by which commodification may occur, and show how this may restrict the range of goods and services that are subject to commodification, therefore having implications for the use of commodification arguments in political theory. Commodification arguments assert that some people’s trading a good or service can debase it for third parties. They consist of a normative premise, a theory of value, and an empirical premise, a mechanism whereby some people’s market exchange affects how goods can be valued by others. Hence, their soundness depends on the existence of a suitable candidate mechanism for the empirical premise. The ‘motivation crowding effect’ has been cited as the empirical base of commodification. I show why the main explanations of motivation crowding – signaling and over-justification – do not provide mechanisms that could underpin the empirical premise. In doing this, I reveal some requirements on any candidate mechanism. I present a third explanation of motivation crowding, based on the crowding out of frames, and show how it fulfills the requirements. With a mechanism in hand, I explore the type of goods and services to which commodification arguments are applicable. The mechanism enables markets to break down ‘shared valuations’, which is a subset of the valuations that proponents of commodification arguments are concerned with. Further, it can only break down relatively fragile shared understandings and therefore, I suggest, it cannot support a commodification argument regarding the sale of sexual services.