by word of mouth
US /baɪ wɜrd əv maʊθ/
UK /baɪ wɜrd əv maʊθ/

1.
口耳相传, 口头传播
through people telling each other rather than through advertisements, etc.
:
•
Most of our business comes by word of mouth.
我们的大部分业务都是通过口耳相传的。
•
The news spread quickly by word of mouth.
这个消息很快就通过口耳相传传播开来。