Sustainable marketing aims to encourage consumer behaviour that will improve the environmental and social outcomes of consumption. Despite decades of effort, however, manufacturers and retailers often see disappointing shopper responses to their sustainable marketing efforts. This paper argues that this is because many sustainable marketing efforts are hampered by false assumptions about how buyers behave in retail settings. The purpose of this paper is to take two commonly accepted sustainable marketing retail beliefs—that ‘sustainable’ brand buyers are a different type of retail shopper and that they are more loyal to these brands than shoppers of non-sustainable brands—and draw upon two established marketing empirical generalisations, the Law of Brand User Profiles and the Law of Double Jeopardy, both built over decades of research, to show that these beliefs are, in fact, myths. We use 22 sets of continuous data spanning five categories in the UK to illustrate this. Mean Absolute Deviations were used to compare the profile of sustainable brand users against non-sustainable brand users. The Dirichlet model of buyer behaviour was applied to the data to examine loyalty to sustainable brands. The results show sustainable brands are just like all other retail brands in their performance. This is a positive finding as it means they can utilise ‘regular’ brand growth knowledge to increase their market share. Overall, the paper illustrates the process and benefits of moving to a view of sustainable marketing that has stronger scientific underpinnings and that leads to more realistic shopper response expectations for retailers and manufacturers.