Improve the offer before the person can decline, so the improvement reads as a concession requiring reciprocation.
Burger's 1986 finding. It works because the improvement is unilateral, which triggers reciprocity, and because it forecloses the moment at which a decision would have been made.
In practice
- A stallholder names a price, pauses, and adds a second item before the customer has answered, and the customer buys.
- A salesperson who adds free delivery before the customer says no has bought a reciprocation the same discount would not have bought after.