A monopoly seller advising buyers about which of two goods fits their needs may be tempted to recommend the higher margin good. For the seller to collect information about a buyer’s needs and provide truthful advice, the profits from selling both goods must be similar enough, i.e., within an implementability cone. The optimal regulation controls pricing distortions and information‐collection incentives separately via price regulation and fixed rewards respectively. This no longer holds when the seller has private information about costs as both problems interact. We study whether competition and the threat by buyers to switch sellers can substitute for regulation.
