✔ 最佳答案
直譯 : I don't know the purpose of this thing. Someone just bought it from us.
但是, 這東西是由你賣給別人. 若就此直接說你不知道這東西, 會有點奇怪.
除非, 你只是該店的收銀員. (注意 : 銷貨員是應該會熟悉產品的.)
因此, 這樣說會比較好 :
I am only a cashier of the shop. So, I don't know the purpose of this thing. Someone just bought it from us.