tough as nails 极为强硬（成语）
英文释义
Extremely stubborn, determined, and unyielding. (NOTE: often used in reference to someone’s negotiation style)
例句
We tried to buy a car for less than the original price, but the seller was as tough as nails, and he refused to give us any discount.
我们想以比原始价更低的价格买一辆车，可是销售人员极其强硬，拒绝提供任何折扣。