Marketing experts are tasked with making important decisions that influence firms' performance. Some decision tasks are decomposable and can be broken down into smaller parts (e.g., pricing new products). Others are non‐decomposable and are challenging to break down (e.g., selecting creative work for advertising campaigns). The literature remains divided on whether expertize aids decision‐makers in addressing these different decision tasks, as well as how different decision‐making processes (critical analysis, intuition, introspection) improve decision‐makers' performance when they face these tasks. Using experiments with comparative samples of senior marketing managers (experts) and general public participants (non‐experts), we test whether expertize provides advantages when making decisions. Our results suggest that experts perform better than the general public with decomposable decision tasks, though not with non‐decomposable decision tasks. Furthermore, decision‐makers who rely on critical analysis perform better compared to intuition when addressing decomposable decision tasks, but the decision process is less important with non‐decomposable decision tasks. These findings provide insight into the conceptual boundaries of marketing professionals' expertize. Managers could apply these insights to potentially save resources (e.g., time, finances) by delegating decisions to more junior staff or even by leveraging external counsel through crowdsourcing.