You're all over-complicating this whole scammed business. Traders used to keep anonymity after a black market transaction because their name was not mentioned, and the food mysteriously disappeared, no message whatsoever.
With the new system, it does not matter what message the lords get, or when. So long as the trader's name is not mentioned. My thoughts on the options presented:
Perfect.
Perfect.
Leave the Trader's name out of the report. Highten security for a short time in case they try again on another of that lords offers.
Tell Seller "The order has been fulfilled here is your X gold, yada yada yada" - all completely true.
Tell Buyer "You have purchased 350 bushels for the price of X. The deal was supposed to have been for 400." Then you throw in a line about either not catching the trader's name, or are provided with a fake one, an alias.
I really like that alias idea, come to think of it. Just imagine "You have purchased 350 bushels for the price of X. The deal was supposed to have been for 400. You are told the trader's name was Ben Franklin, but you cannot find any record of him." The only restriction would be it cannot use a family name of anyone, and preferably not the given name of any character on that particular island.
I disagree with the part where you say to inform the buyer that the deal have differences.
A message saying "your buying offer was filled" to the buyers and "your products were sold" to the sellers is more than enough.
Also we could get a history of the food income and outcome in the granary. This way only those who track down their business will realize that they were stolen.
Also I don't think that "create" a profit in a trade must be something made in the black market.
I'm playing as trader and this is something that really hurt the profession. But I will talk more about this in the proper post.
Another thing that could be done is the trader simply buy the food from anywhere and then be able to create a fake offer in any market to sell it latter. It would be a black market action because you are not a lord. Also this could inform, to the buyer, that the food would come from a random region. This way if the lord care from where the food comes, he may talk with the other lord to confirm its origin.
