Victims of fraud are almost always attracted by expectations of exceptional profit. They succumb more to their own greed than anything else. A deal which is too good to be true probably isn't true - yet people around the world queue up every day for all manner of schemes which could not logically be genuine.
Grains and sugar are openly traded on all the world's major commodity exchanges and their prices are exactly established. There are some long-standing international grain and sugar traders of the highest repute. Offers to sell products at less than the ruling market price makes no commercial sense - unless the real motive is fraud.
This has been a standard ploy since time immemorial: to make the victim believe that he has access to a phenomenal deal; so good that he wants to keep it secret. This enables the fraudulent seller to conceal detailed information about the origins and location of the sugar or grains. The buyer thinks he is on to something no-one else knows about, which will make him a quick profit, and doesn't care too much about the origins of the product or why it is cheap, so long as it is genuine - and the documents appear to protect him on this point.
To allay suspicions a fraudulent seller will often offer various assurances which seem to give protection, or at least to vindicate his character. He may lodge a performance bond equal to, say, 2% of the value. He is then risking 2% in the hands of an honest buyer in order to swindle him of the remaining 98%. He may provide various attestations from banks as to his financial worth (of no legal value or protection). He may offer to supply secret information about the exact location and origins of the product in return for, say, 10% part payment, either as a means of consolidating the deal or simply to abscond with the part payment. Provision of unnecessary quasi-official documentation is another tactic; any bit of paper which seems to confirm the existence of the goods provides further re-assurance.