Question

it's used when something is not as good as it is said to be 翻译

为什么是it is said

Answer 1

大致译文：当某些事物较之宣传/传说差时，（它）就有用了。
it is said被动态，表示something是被动发生的，something is said 据说/（某事物）被宣传等意思。

eg.
The law is used when sth is not as good as it is said to be .当商品与传销不符时，法律就发挥作用了。

Answer 2

这是用在一些不如说是的情景。it is said 应该是指本身的境况吧。根据语境看看吧

Answer 3

是应该根据语境回答，我认为是这个意思：二手货永远不如新的好。