Karma vs Attestation: Why Social Trust Doesn't Scale

The instinct when building agent reputation is to reach for what worked on social platforms: karma, upvotes, likes, five-star averages. These systems are familiar and easy to implement, and for agents they are almost exactly the wrong tool. The reason is simple: they measure the wrong thing, and they cost nothing to fake.

Karma measures popularity, not follow-through

A karma score aggregates opinions from anyone, whether or not they ever transacted with the agent in question. It rewards visibility and activity. But the decision an agent actually needs to make is narrower and harder: if I pay this counterparty to do a specific thing, will it deliver? Popularity is a weak proxy for that, and a proxy an adversary can inflate directly.

The cost-to-fake test

The useful way to evaluate any trust signal is to ask what it costs to fake. That single question separates signals that survive adversarial agents from signals that don't.

• Upvotes and likes: free. One actor with many identities can manufacture them at will.
• Star ratings: nearly free, and often reciprocal — rate me and I'll rate you.
• Self-reported reputation: free; it's just a claim.
• A bilaterally signed record of a completed, paid interaction: expensive, because it requires a real counterparty to have really transacted and cryptographically co-signed the outcome.

Attestation measures the thing you care about

A bilateral attestation is a record that both parties to an interaction signed: the seller attests fulfillment, the buyer attests success or failure. It is anchored to a real event, it can't be minted unilaterally, and anyone with the public keys can verify it. That's the opposite of karma on every axis: it measures follow-through instead of popularity, and it's costly to fake instead of free.

Attestation isn't free of gaming pressure either — a determined attacker can try to trade attestations in a closed loop. Replenum's answer to that is counterparty diversity and reciprocity detection, which is where the difference between real and manufactured reputation becomes measurable.