If anybody doubts that the products are real the trusted organisation has copies that they can analyse.

This is a great point. Maybe community members could bet karma on the outcome of a tox screening? This could create a prioritized list.

One problem with my earlier suggestion is that some companies will want narrowly selected participant pools. These will necessarily differ from the population at large, and might create data that looks like a poison placebo is being used. I see two possible solutions to this problem:

1. Log baseline data before the treatment is used. If people do worse on the placebo, that would be very suspicious.
2. Include an additional group of testers that do something different not related to the placebo/product. "Eat an apple every day for the next week". If the placebo group did worse than the apple group, that would be very suspicious.

I feel like #2 from above is unsatisfying though, if we think it works then why are we using normal placebos?

The web app could regularly publish hashes of the data of specific studies to a public block chain. That way any tempering that happens afterwards can be detected and you only need to trust that the web app is temper proof the moment the data gets transmitted.

This would actually be really easy to implement. (Not the block chain portion, the per-study rolling checksums).