Contingent valuation approach has been criticised as fundamentally flawed because it fails to address the impact of protest respondents on the economic valuation exercise. In this study, we present results from an analysis of the factors behind protest responses in willingness to pay exercises for biodiversity conservation (non-use values) and ecosystem services maintenance (use values). The influence of the payment vehicle for stakeholder groups was also explored considering different contributions for conservations purposes, which included donation, 0.7% of income, willingness to give up time, and no possible contribution. The study was conducted in areas involving the only two national parks in Andalusia: the Doñana social-ecological system (SW Spain) and the Adra-Nacimiento social-ecological systems (SE Spain). Protest responses have been shown to reveal a great deal of information that should be considered for designing conservation policies. We found that the possibility of receiving protest responses related to implementing a payment for maintaining ecosystem services was higher than for biodiversity conservation and may vary according to respondents' socio-demographic characteristics, pro-environmental attitudes, and stakeholder typology. Generally, more of the efforts of environmental education programs regarding conservation policies should be aimed at older people with lower education levels and men. Furthermore, future strategies for conservation should consider individuals' willingness to give up time for protection and restoration activities as a useful option.