Well, refusing to consider the idea that someone might do something with more than zero layers of subtlety... would lead to falling for every trick anybody ever tries to play. ;) A more appropriate response would be to admit that it's not easy to tell the difference, and maybe, if the interlocutor cares enough, to do some research to determine whether or not it's still suspicious once the facts are known. One example of some facts that could resolve or strengthen the suspicion would be: How many other emails of equal or greater verbal strength were sent at Google, but then not followed up by dismissal?