In this pre-registered experiment conducted in the Netherlands and Türkiye (N_total = 550), we investigated how the source of advice (peer vs. expert) influences people's decision-making when assessing the carbon footprint of a flight between two cities. We also examined whether this effect was influenced by their conspiracy mentality, collective narcissism, epistemic individualism, and climate change scepticism. Our findings suggest that people overall rely more on experts' advice than peers', especially in the Netherlands compared with Türkiye. Moreover, individuals high in conspiracy beliefs, epistemic individualism, and collective narcissism reduced the weight advantage typically given to expert advice over peer advice. Only a specific form of climate change scepticism (i.e., trend scepticism) showed similar effects. Overall, our results indicate that individuals who value their own opinion and harbour distrust towards experts or science tend to discount expert advice.