Complex sentence: You must tell your trading partner (publicly, so other opponents may hear) truthfully what two of the three are, and you may declare the third truthfully or not as you please; it is the "bluff".
Split into simpler sentences: You must tell your trading partner (publicly, so other opponents may hear) truthfully what two of the three are. You may declare the third truthfully or not as you please; it is the "bluff".