Well, it depends entirely on the contract between the farmer and the reseller. If the contract states you get the retail price minus 5% and I lie to you about the retail price, certainly this is fraud. But if the contract states you get $X/pound, and that's exactly what I pay you, the retail price never enters into it.

If later on the farmer complains that they were paid according to the contract terms, but their meat is retailing for a higher markup than they expected because of its enticing packaging, I don't see how the farmer is entitled to any relief on that.