"Grant I may never prove so fond
To trust man on his oath or bond."
-Shakespeare, Timon of Athens, I.ii, lns. 64-65
This is meant in jest, as part of a tongue-in-cheek dinner song, and yet so many misadventures begin with the phrase, "You can trust me." Please note too that this is a phrase usually punctuated with the suffix "I'm an expert."
Whenever someone asks you to trust them because they're an expert, run the other way.
To trust or not to trust. Which is more human? Animals trust each other all the time. The survival of species is dependent on cooperation. Interspecies deception is commonplace, whether through behavior or genetic adjustment, but intraspecies deception is far more rare. Two leopards may compete for the same mate, but they're not sociopathic about it.
Who is the greater fool - the man who trusts implicitly or the man who believes that every word he speaks is trusted and believed? Skepticism is healthy, but isn't a person who doubts the virtue and veracity of everyone and everything just as much a fool as the two men aforementioned?
Then again, raise your hand if you always trust yourself.