Question about using real time demos

So I have a question, far as I know we get to use some of the assets for free, but my question is someone allowed to use any/all the assets such as “Infiltrator” as their own game trailer, for their game, but only change the two characters in it?

I just wanted a better understanding how things work, and what’s allowed or what’s not not allowed to use as their own project for commercial use.

You could, but people will have a very negative reaction

Doing that will hurt your reputation badly, someone will find out and he will expose it to the rest. On Steam Greenlight there are people doing this already.

And there is no need for that, visit the ArchViz forum and make something similar, many videos just use simple Matinee movements and transitions and still look amazing.