Right right, but so is Ace. In fact, he's also able to sniff out other people's deception rather easily.
Punkjack is a rider joining one DGP, who's actually part of the DGP's staff that had filled in for a prior DGP due to a lack of available players since the next contest was done in pairs. Punkjack then and Punkjack now is very different (the former being a literal mute no-nonsense guy and the latter being a ******* rock star). Despite being able to convince others that this Punkjack and he are actually different people, not only does Ace see through his lie, but he also finds out that he was ordered by the current Game Master to take him out of the DGP, to the point of not even writing a wish when he starts participating, at which only he knew. All in the span of a few seconds when he saw Punkjack and the navigator of the DGP together in a hidden area of the maze (she had to join as the hostage, thus her temporary participation).
Ace was also able to completely figure out the true nature of the DGP while fighting a completely different Rider (the future people obviously were spectating). These are just some examples.
If it helps, the only time he was completely taken for a ride was when Keiwa pretended to fight and lose against Ace to draw out Girori the Current game master of that DGP so that he can reveal himself to be caught by the higher-ups. This is only because:
- He knows Keiwa well enough to believe that he's serious about beating Ace and getting his wish for world peace. Keep in mind that Keiwa has participated in the previous DGP where silent PunkJack had taken part and also has been saved by Ace before he joined the DGP.
Keiwa's a bloody tanuki to Ace's fox
Thus, actually deceiving him is going to be incredibly hard, while Ace has more than what it takes to see through him (the deception part, I mean). Mera didn't steal his intellect away for nothing.