BOGO (“buy one, get one” free or discounted) is a multi-buy promotion that increases the number of units a shopper leaves with. Its honest form is a legitimate volume deal — a seller genuinely passing along savings on things you’d buy anyway, like household staples. It turns manipulative when the base price is quietly inflated so the “free” second unit is already paid for, or when the framing pushes you to overbuy perishables and slow-moving stock you didn’t need.
Two mechanisms do the work. First is the “free” effect (Ariely): a second unit labeled free pulls far harder than the same value expressed as “50% off two,” even though they can be arithmetically identical. Second is anchoring and value perception — the promotion sets your reference point at “two for the price of one” rather than at the true per-unit cost, so the transaction feels like a win regardless of whether you needed two. Retailers frequently pair BOGO with a base-price bump timed to the promotion, and sometimes make the “free” item a near-expiry or low-demand SKU they want cleared.
The countermeasure is simple arithmetic plus honest need-assessment. Divide the total for both items by two and compare that real per-unit price to the ordinary single price and to other stores; check whether the single-unit price rose just before the deal. Then ask the harder question: would you buy the second unit at its true cost if it weren’t dressed as free? For perishables, two is only a saving if you actually consume both. A BOGO that survives this math is a real deal; one that only looks good because of the word “free” is selling you volume, not value.