Cialdini reciprocity principle (Influence; 240+ peer-reviewed papers) — one of the most robust, cross-cultural principles of influence; formal articulation: Gouldner 1960

Claim: Robert Cialdini's body of work (Influence; 240+ peer-reviewed papers) establishes reciprocity as one of the most robust, cross-cultural principles of influence: people feel obligated to return favours and value given to them. The norm was first formally articulated by Gouldner (1960).

Source: Cialdini, Influence: The Psychology of Persuasion; Gouldner (1960), "The Norm of Reciprocity," American Sociological Review.

Confidence: Verified / Industry-consensus.

Caveat: Reciprocity online is low-cost — the "favour" is ambient. A free tool likely produces diffuse goodwill / brand warmth more than a strong one-to-one obligation. Strongest when the free value is genuinely substantial (a real estimate the user would otherwise pay for); weakest when "value" is a thinly veiled lead-capture gate.

Why this matters for Candid: Anchors the trust argument for ungated tools (R2 — Default to a directional range, ungated, with a loud "this is a ballpark" — not a precise gated quote from Brief A). Tools that gate the result behind an email capture invert the mechanism — the user no longer perceives a gift, they perceive a transaction.