You bid, you buy: It's crucial for the integrity of an auction; when you make a bid on an item, you should be prepared to go through with the purchase. Initiating chargebacks or canceling purchases could potentially result in a ban.
No artificially raising prices through bidding: You can only place a bid if you have a genuine intention to acquire the item. Any evidence of attempting to artificially inflate prices through bidding will lead to a permanent ban.