Sellers pick either reputation or a certificate to prove quality—but which one works depends on the item's value.

When you buy items online, it is hard to know if a seller is telling the truth. Buyers usually rely on two things: a seller's personal reputation or official verification from an outside expert. Researchers studied nearly one million fixed-price eBay listings of Pokemon cards to see how these two systems work together. Sellers could pay an expert to grade a card, grade the card themselves, or give no signal. The researchers found that highly trusted sellers gain a bigger price boost when they grade items themselves, but extra trust does not increase the boost from outside certification. Because lying damages a good seller's reputation later, trusted sellers can successfully grade their own items instead of paying upfront for an outside expert.

Why it matters

Every time you buy something online from a stranger, you rely on trust. This work shows that trust isn't a single choice between reputation and a certificate—it's a sliding scale. For cheap items, reputation alone might be enough; for expensive collectibles, a certificate pays off. That changes how marketplaces design trust systems and how buyers decide what to trust.

Questions answered