Why one-per-customer raises the average purchase

A sign reading limit two per customer appears above a promotion and purchases rise. Not among the few who wanted three and were stopped, but among the many who had intended one and left with two, having read the sign as guidance rather than as a constraint on their behaviour.

What everyone sees

A purchase limit is understood as a restriction. It holds sales down, it protects stock, and it exists to stop a small number of buyers from taking everything. The people it was not aimed at are assumed to be unaffected, since the ceiling sits above what they wanted anyway.

What is actually happening

Studies of purchase quantity find the limit acting as an anchor. Most buyers arrive without a considered number in mind, so a figure printed on the shelf becomes the reference from which they adjust downward, and the adjustment is insufficient. Work on restrictions in promotions found the same sign also raising perceived deal value, so the limit performs two jobs at once.

Why it stays hidden

It is concealed by resembling its own opposite. A restriction cannot easily be accused of encouraging purchase, and the retailer can point to the ceiling as evidence of restraint. The buyer, meanwhile, experiences a decision made freely: the anchor arrived before any deliberation, so there is nothing in memory to which the second unit could be attributed.