how do you verify that it works the way they say it works

Open source -> you look at the code

a source code repository on github does not have any guarantees that they are distributing the software built from exactly that source code.

but even worse, almost all such apps are closed source. and you have no chance to verify what runs on the server in either case.

how do you make yourself heard when it doesn’t

In proper domcratic counties that is what law is for.

is this “law” thing you mentioned able to make your thoughts appear telepathically in the minds of millions of others, without a channel like the internet?

are you going to post to facebook with your discovery and hope millions will see it and agree with you?

or are you going to grab a big board and a megaphone and go to the town square about the problem?
this is probably the more effective way, but you’ll be called obnoxious, especially by those who have no idea about the tech they use