This paper presents data conducted to analyse consumer behaviour in agri-food markets, where product differentiation failures occur, with the aim of disentangling the roles played by both consumer information and inferences made from informational stimuli. We thus examined consumer knowledge structures and brand credence related to attitudes towards a particular foodstuff and a product alternative, as well as the actual consumption of the foodstuff. To do so, the selected case study was the olive oil markets in Spain, given that products such as extra virgin olive oil (EVOO) and refined olive oil (ROO), that differ in terms of intrinsic features, become undifferentiated. The data of the observed variables were collected from 700 regular buyers from an online panel at the household level in southern Spain. The data were processed using both Excel for checking, cleaning and descriptive purposes and ADANCO 2.0 for performing the model estimations.