The pharmaceutical gift literature is the cleanest field evidence for reciprocity in existence, because it has a measurable output.
Physicians who receive gifts from drug companies — meals, samples, sponsored travel, speaking fees — prescribe differently afterwards. The effect has been found for formulary requests, for prescribing volume, for brand-name over generic selection, and it has been found at very low gift values, including single meals costing under twenty dollars.
The finding that matters for defense is the second one. Physicians surveyed about this consistently report that their own prescribing is unaffected, while believing that their colleagues' is. The behavior moves and the self-report does not.
That gap is the entire reason this chapter recommends a rule rather than vigilance.
Introspection cannot detect reciprocity pressure. Regan's 1971 experiment, chapter 1, established the mechanism: the obligation operates whether or not you like the giver, whether or not you wanted the gift, and whether or not you approve of the exchange. The subjective experience is not I owe this person; it is a mild, unattributed discomfort that resolves when you comply.
The early signals are worth naming because they are specific. A feeling of obligation toward someone you met recently, which you cannot account for. Reluctance to give an unfavorable answer to a person who has been generous. Finding yourself explaining why the thing they want is actually reasonable. And the tell that catches the timing: a gift that arrives before an ask rather than distributed unpredictably across a relationship.
The detection protocol is a single question asked at the moment of offer rather than at the moment of decision: who benefits if I accept this, and what is the ask likely to be.
The counter-response has three options and the first is much cheaper than it sounds.
Decline at the point of offer. Refusing a gift is momentarily awkward and permanently free. Resisting the obligation later is neither.
Reciprocate symmetrically and immediately, which discharges the debt: pay for the lunch, send something of equivalent value, do a favor back. This is why some professions require that hospitality be reciprocated or reimbursed.
Or disclose, which is what conflict-of-interest rules are for and why they work: the obligation is not removed but it is made visible to everyone assessing your decision, including you.
This counters Law 2.