不怕不识货，只怕货比货
bù​pà​bù​shí​huò​zhǐ​pà​huò​bǐ​huò

quality is best judged by comparison

不怕不识货，只怕货比货 不怕不識貨，只怕貨比貨 bù​pà​bù​shí​huò​zhǐ​pà​huò​bǐ​huò
quality is best judged by comparison
literally "don't worry about not being able to judge the quality of goods, only worry about comparing one item against another"; a proverb meaning that the true value of an object or person can only be determined through direct comparison