Depends on how it was set up. 'Smile Guy' very well might have known his rule before he got into the game. And that he would be used as a proxy for the Smile to talk. With an absolutely massive reward to be had, he might have thought it was worth the risk. But I bet he didn't know about the box of truth thing, so that was very much a gotcha moment that got him killed.
We did. Infinite's secret was that someone had entered the game under false pretenses and that you get 5 mil for identifying them and another 5 mil for killing them.