Shop advertised a big discount but the was-price looks made up

Inflated was-prices can breach the Fair Trading Act 1986. The Act prohibits misleading and deceptive conduct in trade and false representations about the price of goods, and a reference price that was rarely or never charged can give a false impression of savings. Regulators generally expect the higher price to have been a genuine price for a meaningful period. Keep the advertisement, your receipt and anything showing the price history. You can complain to the Commerce Commission, which enforces the Act and can prosecute. On a personal level, you may have a claim for the value you were misled about, but recovering a small difference can be difficult. If the sofa is also faulty or not as described, your rights under the Consumer Guarantees Act are separate and often more useful.