a pig in a poke
掩人耳目的买卖或交易，即对商品的真实情况毫无了解
口语·书面语·警告未检查就购买
英文释义
buying something without inspecting it first
例句
Buying a used car without a test drive is like buying a pig in a poke.
典故来源
源自中世纪市场骗局：卖家将猫冒充猪放入袋子出售，买家未检查就购买，结果上当。