To take something with a grain (or a pinch) of salt means not to completely believe something that you are told, because you think it is unlikely to be true.

For example:

You have to take everything she says with a grain of salt, because she tends to exaggerate.

All parties make many promises before elections, which should be taken with a grain of salt.

I’m taking his article with a grain of salt because it seemed to be specifically crafted to promote more drama.

Please take what you read with a grain of salt. Use your common sense and consult your doctor.

I always took the rumors with a grain of salt.

Sue says the internet is great, but she takes a lot of the information there with a pinch of salt.

Tradução: ficar com o pé atrás, ficar desconfiado, ter cautela.