buy the case (/casket)and return the pearls (/jewels) —be ignorant of the value of a thing; show lack of judgement; make the wrong choice
? 不善讀書者，昧菁英而矜糟粕?！m多奚益？(裘廷梁 《論白話為維新之本》) Those who do not know how to read fail to see the essence but talk big of the dross. Such lack of judgement is just like buying the casket and returning the pearls to the sellers. What use is there reading a lot like that?
買櫝還珠mai du huan zhu
keep the glittering casket and give back the pearls—show lack of judgement
買櫝還珠mǎi dú huán zhū
櫝：木匣子；還：交還；珠：珍珠。買下木匣子，卻又把里面裝的珍珠還給人家。比喻沒有眼光，取舍不當。show lack of judgement, make the wrong choice