Labels signaling sustainable product attributes are gaining importance, although uncertainty concerning the environmental, micro-and macroeconomic benefits of such labels persist. One of the questions still incompletely answered is whether Willingness To Pay (WTP) varies with a gradually increasing number of labels on a food product. In order to answer this question, we conducted a laboratory experiment with 191 student respondents, testing consumer valuations of different labeling strategies. Using the Becker-DeGroot-Marschak mechanism, WTP for 15 food products was measured. The products were endowed with up to six different sustainability labels, such that each grocery item was available in eight product versions. For perishable, non-perishable and plant-based products, the results indicate that participants are prone to allocating WTP-premiums to labeled products, more than to unlabeled products. For animal products, however, labels do not influence WTP significantly. Furthermore, the premiums do not vary with an increasing number of labels, irrespective of whether the labels signal substitute or complementary sustainability information. The results are not entirely in line with normative notions of magnitude variation, but rather with the behavioral economic concept of embedding effects.

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Questioning the external validity of experiments that rely on student participants is an evergreen in experimental economics. Yet, there is ambiguous evidence of potential subject-pool bias. We add to the subject-pool debate by enlarging the set of experiments for which subject-pool differences have been studied. In a duopolistic Bertrand market setup designed to test for collu-sive behavior, we test two treatments. The first i s a b aseline t reatment, w here p articipants cannot communicate with each other, the second is a communication treatment in which participants are allowed to communicate. Each treatment is first conducted with students and then replicated with professionals. Our results show that student subjects and professionals differ significantly. However, these differences manifest themselves in quantitative rather than qualitative terms. Professionals do collude more, but their behavioral difference between treatments is similar. Students are thus a valid surrogate, if the research question is qualitative, but results generated by student samples should be handled with caution, if quantitative differences matter.