I have not seen this scenario, but I assume that a blockchain could more reliably and believably be made public, recording all the way down to the farmer, then could other technologies.
Blockchain enables transparency from the farmer to the consumer. It does not ensure that the farmer was not coerced.
To make it simple to understand:
For example, international conglomerate using exclusively slave labor inputs "these bananas are small farmers fair trade bananas" into blockchain.
That's it. That is the "transparency".