Previous research suggests that contextual factors can affect the perception of food products, however, we still know little about how consumers evaluate these items in terms of sustainability. This research investigates how well shoppers can rate food items in the matter of their environmental impact, whether they are overconfident in their knowledge of food sustainability, and whether labels on packaging and great availability of choice can affect their judgment. Through an online behavioural experiment, we test the impact of salient truthful and untruthful green labels, and of choice overload on people’s perceptions of the environmental quality of food products. We find that choice overload is detrimental to consumers’ judgment, but that truthful labels can help shoppers correctly identify sustainable items. However, untruthful labels can negatively impact consumers’ judgments with choice overload, even if shoppers have greater prior knowledge of sustainability. These findings suggest that truthful and untruthful salient labels and choice overload can have an impact on shoppers’ perceptions of food products. We find that overconfidence in one’s sustainability judgment is negatively correlated to judgment accuracy. Hence, great care should be taken in presenting food products to consumers to make the most environmentally friendly items stand out.