The blockchain would be a decentralized papertrail accessible to all actors of the supply chain, down to the end consumer ideally, instead of the current nightmare of shipment papers, siloed ERPs and so on
bad actor: I manufacture the cheaper rolls, and stick labels for the expensive ones on, and scan them
How will "the blockchain" prevent either scenario
Bad actor: unless you intend to use rolls by yourself, what do you gain? You can't sell the better rolls as such, because you have broken chain of trust.
But such arguments lead nowhere. Of course you can come up with scenarios which can be misused. The real challenge (and one that is being solved by lots of people in crypto world - well, at least those that aren't consumed by greed) is finding scenarios that work. The ability to store information cheaply and immutably can change many industries, but technology must be deployed in such way that it makes sense.