Some guy in the honda shop said that if you put your iat sensor on your cold air intake you would gain more power is this true or false if so please explain

 

Yes. You would gain marginal, useless power. Since it measures intake air temp, and the colder the air teh denser it is, it would in theory give you more fuel to mix with more air, thus more power. The problem in tricking your car though, is it may run rich if the air heats up too much between the intake and the throttle body, due to heat soak on the piping.