Yes. It is possible to verify what’s going on. That’s what I did when I used the aur. Do you think most people do that, or even look at see how many users are using the software? Or do you imagine they just install it blindly?
If you ever see a help video or article that suggests installing something from source, or run some script people generally tell the reader that they shouldn’t just run random code without looking at it. I’ve never once seen anything that suggested people should check the pkgbuild. I don’t have a problem with the aur. I just think it’s not nearly as trustworthy as it’s generally made out to be, and I don’t think people generally understand that it might even be a concern, or that you can check the validity of the package yourself.