Koaba, Merchant of Dran

Defender, Ward {3}
When a non-artifact enters the battlefield, you may pay {1} to put a For Sale counter on it. As long as it has a For Sale counter, you control it.
Other players may spend {x} to remove X For Sale counter from an artifact you control and gain control of it; You create X treasure tokens. Any player may spend X to counter this ability and put another For Sale Counter on the artifact.
Sacrifice an artifact you control: Gain 1 life and draw
a card. Use this only during your upkeep.