Talk Is Cheap Meaning

(idiomatic) It is easy to make boastful or unrealistic statements which are not supported by actions or evidence.

Example: 1915, Jack London, The Star-Rover, ch. 2,
  Cecil Winwood accepted the test. He claimed that he could dope the guards the night of the break.
  "Talk is cheap," said Long Bill Hodge. "What we want is the goods. Dope one of the guards to-night."