Yes Occam does quite literally state that – the option with the fewest assumptions is most likely to be correct. Assuming that someone is lying is an extra assumption to make over what they are claiming to do.
Malicious acts from large corporations are certainly well known, but they're also grossly over-represented in the news and mindshare. Mostly things just work as they say they work.
I don't really know what proof you're looking for, it's well known that it's hard to prove a negative. I'm not suggesting taking Google (or anyone else) at face-value, but rather saying that when you think about T&Cs, laws, PR, etc, it's unlikely.