Take it with a grain of salt.

If you 'take something with a grain of salt,' it means that you consider the source while deciding if something is true or not.

Examples:

-Sara didn't like the movie.  She said it was awful.

-yeah, but you have to take everything she says with a grain of salt.  She doesn't like most movies.

-The newspaper said the economy is sinking.

-It could be true, but you have to take it with a grain of salt.  That newspaper isn't very reliable.