Clemenza may have been more street smart than tessio. As seen in g2, he was already running scams on his own before be met vito and tessio. When all 3 started running together, their combined experiences started everything. Clemenza knew not to double-cross the boss no matter how unhappy he might have been at that time. There is a lot on the screen that is self-explanatory and alot that you have to surmise that MAY have happened as the posts here show. Clemenza MAY have been told that Carlo was being given that bogus position to set thing up. Clemenza MAY have been told how to act in the meeting in the den with the key players to trick Tessio into thinking everything is going as planned. If Tessio was ao confident with his play, why is he so concerned when he gets off the telephone in the kitchen, that when he turns around and looks at Tom, he has a look on his face that expected to get whacked right then and there. When they go outside, when he finds out what is going to happen, he never saw it comong.