schema.org – How to prove that third party evaluations and evaluations are correct and real?

we are developing an application that of course has a website.
I've added some of our user ratings and ratings given in Google Play, Apple Store and the corresponding JSON-LDs.
Individual Evaluation Example (Review -> Rating).
Example of global comments (UserReview -> AggregateReview)

I could not find the answers on the internet where there was more information about falsification of the data. For example. make your rating 5/5 of 1000000 people. I would not want to pretend then some questions arose:

  1. It's the site developer who can add data that can be false or real.
    How can I prove the authenticity of a user notice? Link to the third party site where the revision exists? Any other way? In both stores, there is a link "Link to this review". Is it possible to link the individual note to this link?

  2. We now have 15 Apple Store ratings and 12 Google Store evaluations. So we got an overall score of 5 on the Apple Store and 4,833 on Google Play => average 4 9165 => ~ 4.9. A page may have an aggregate rating, but what about now when the rating comes from two different sources?

Then I tested them with Google's test tool: https://search.google.com/structured-data/testing-tool/u/0/
and some questions have arisen.

  1. Who is the author of AggregatedRating if the notes are added by me, but that they actually come from Google and Apple? Since this is a mandatory field or the test tool generates at least one error, "a value for the author field is required". because I leave it empty for the moment.