Why aren't these faces extruded as the tutorial video? I was following a YouTube tutorial, and when the presenter "hit 's' and scale forward...", they looked like the first screenshot below. But when I did that, the direction that those faces were extruding to were different as the second and third screenshots below. Notice the bottom low faces; they are extruding upwards, instead of downwards as the tutorial. Why is it so? The blender project file is here.
You have a lot of overlapping vertices which seem to be effecting the scaling operation.

To remove these:


In Edit mode select All of the model.
Open the Vertex menu.
Select the Merge Vertices.
Select the By Distance option.


At the bottom of the screen you will see how many vertices have been removed.



Now re select the 8 faces, and they will scale as shown in the video.