Agency, The Starting Point

Last week I realized that law of agency must be overlooked by agents, especially in the commercial market.  You'd think that agency and who represents who would be easy to spot....but when I called one agent on a possible referral, he didn't realize that I too would be an agent representing the same client on the same side of the transaction.  The other agent didn't have an agreement representing his client and when I asked him whether he represented the seller or the buyer, he realized his error but got mad at me for trying to sort it out.  As it turned out, he represented the buyer.   If I understand it correctly, if not stated, I automatically represent my broker and his listings, making me a representative for the seller, and unless I get a buyer's representation agreement, the buyer has no representation.  I can't represent both the buyer and the seller in the same transaction.