huàn huò shí, zhòngdiǎn búshì zài jiǎng yīcì jiàgé, ér shì zhèngmíng zhè shì tóng yī bǐ gòumǎi

换货时，重点不是再讲一次价格，而是证明这是同一笔购买。

When exchanging goods, the focus isn't on re-explaining the price, but on proving it's the same purchase.