Sellers pay to be trusted when no other signal vouches for them

Evidence

This could suggest, in line with Dasgupta’s argument (this volume), that with respect to that particular transaction the protection the mafioso offers is really a public good which benefits both sides. If he did not act as guarantor the exchange would not take place at all, for the potential buyer would be deterred from entering the transaction for fear of getting a bad deal. The seller’s tip, in other words, might reflect the price he is prepared to pay to be trusted. — Diego Gambetta, Trust - Making and Breaking Cooperative…, 2240

Categorization

• XREF: Directly parallel to Hardin: trust collapses without observable constraints; here the buyer needs the mafioso’s guarantee precisely because seller fidelity is unobservable. Also echoes the blind-world readings where only one sighted agent can certify others.
• QUESTION: Does the seller paying to be trusted indicate the guarantee is a public good even across both parties, or merely a two-sided private arrangement?