lǐyóu bù xūyào hěn fùzá, zhǐyào ràng duìfāng zhīdào nǐ wèishénme xiǎngyào zhège jiàgé

理由不需要很复杂，只要让对方知道你为什么想要这个价格。

The reason doesn't have to be complicated; just let the other party know why you want that price.