But to the extent that any one of those metrics may show that your methodology has a negative or even negligible impact, what mechanisms exist to ensure your fidelity to these metrics, instead of leaning on public relations and marketing that pick up the slack?

No one is here accusing you of doing any of these things. On the contrary, there is an implication that you are positive that you will be able to do these things, even though you're obviously still validating the idea, at some level.

Edit: switched you're for your.