Generally, in Chinese, the phrase "A of B" is translated as "B的A". Eg. A friend of mine. = 我的一个朋友. The method of learning Chinese. = "learning Chinese" 的"The method". = 学习中文的方法. So.. In Chinese, "Closing the Sales" means "成交" (完成交易) Secrets of Closing the Sale. = "Closing the Sale"的"Secrets". = 成交 的 秘诀. Got it?

如果更好听一点，也可以说“成交的秘决”

成交的秘密