These watches look expensive, but they're just cheap knock-offs.

knock-offs 是复合名词，由动词短语 knock off（非正式用语，表示"仿制、抄袭"）加上连字符和复数后缀 -s 构成。knock-off 指"仿制品、山寨货"，通常指廉价模仿名牌的产品。