eBay is the most successful online auction site. In this paper, we study bidding behavior on eBay auctions. First, we show that under the assumption of IPV, the truthful and early bidding is approximately optimal. Then, we compare the truthful and early bidding strategy with the late bidding strategy and point out that the optimal bidding strategies rely on the influence of bidders? valuations, i.e., IPV or AV (affiliated valuations). In the following, we analyze the advantages of the truthful and early bidding strategy from different aspects and the influence of auction components on bidding strategies, such as proxy bidding, bid increment, the number of bidders, and stopping rules. Finally, we discuss preliminary their optimal bidding behavior under the assumption of the hybrid valuations of IPV and AV and obtain some conclusions.