Is it permissible to complete the sale of a commodity to a person proven to be a swindler, knowing that the source of the money with which he purchased the commodity is unknown?

Interacting with someone who possesses ill-gotten wealth can be either forbidden (haram (definition)) or disliked (makruh (definition)). It is forbidden if the transaction directly involves the ill-gotten money itself, whether through buying, selling, accepting it as a gift, or as a loan. However, it is not forbidden if the illicit wealth is mixed with his lawful wealth. The preponderant view is that dealing with someone whose wealth is mostly illicit is disliked (makruh), unless the specific illicit money is identified. It is preferable to avoid dealing with such a person altogether.