Benny tries to get you to leave the casino floor and go to a room to "talk" which is a trap. If you saw it coming, that's fine, but he does lie to you in an attempt to fool you.
It was obviously a trap, if thats his best attempt at making well done liars, well, can't say im surprised.
In fallout 2, after proving your worth and doing jobs to a shady leader for a gang of bad doers, the guy treat you as a good tool for the right job and offer to give you a holodisk containing the location of V13.
Theres no reason to think he is lying, you proved your value, worked your way and paid for the holodisk
What you get is the location of a fake Vault, made out of junk to fool morons into spending money
Once you return to the NCR and tries to talk to the guy (Mark), hes gone.
Earlier in the game you can take a quest to save a city (modoc) in exchange for information, the mayor which said he knew about the G.E.C.K can be persuaded to seal a promise of telling you that, to the point of your char being able to make him cut his pink finger off so he can show how dead serious he was in said subject.
After you solve the entire issue he reveal he was just desperate for help and lied to you about knowing anything about the G.E.C.K
I need to mention the Wright son's murderer quest in which everyone keep pointing out to another suspect, so lies were the main point of the entire conflict?
And yes, i know which parts gonzales is credited for, i just don't know why anyone would think Benny, Caesar or Vulpes are even remotely interesting