No, I do not think that you would have any liability as to the third party.  The buyer did not acquire ownership to the business or the equipment and he would not have until the last payment was made.  The third party was foolish to loan him money without a copy of a written contract to purchase that showed that he had something tangible to put up as collateral.  The loan was between the third party and the potential purchaser.  You have no agreement with the third party.  I would, however, take all the documents that you have, as well as your knowledge of the agreement to purchase, to an attorney in your area and to speak with him or her about it just to protect yourself.  Good luck.