(58) Chapter. A seller should not urge somebody (in case of optional sale) to cancle a bargain the latter has already agreed upon with another seller so as to sell him his own goods; and a buyer should not urge the seller to cencle a barbain already agreed upon with another buyer so as to buy the goods himself, unless they are given permission in both cases, or the bargains are cancelled with the willingness of both the seller and the buyer.