The increasing distributed generation of renewable energy and alternative energy generation technologies is making it important to consider when and how buildings consume energy from a cost and sustainability perspective. If buildings can be flexible in their consumption patterns they can use the greenest and most efficient produced energy and help solve gridside imbalances with cost benefits. Building modeling and simulation can provide an effective method for evaluating flexibility opportunities in buildings. However, most building loads depend on the occupant presence and dynamic interactions between different building components. Therefore, occupant presence and different interactions have to be taken into account when developing the energy performance model and when evaluating the simulation results for flexibility. In particular, this is key in the retail sector which this paper considers as the case. In this paper we present a detailed simulation model of a supermarket, evaluate different flexibility scenarios and discuss the flexibility results in light of an ethnographic study of the work processes and the store operation.