This book presents an empirical analysis of price determinants and bidders' behavior in online auctions eBay.de and Aukro.cz. We focus on the effect of sellers' feedback rating score and the phenomenon of sniping. Buyers in online auctions cannot personally inspect the quality of the product, so they have to rely on seller's honesty. In this setting, seller's rating may significantly contribute to the final price formation. Sniping is a bidding strategy, whereby a bidder waits until the last moment of the bidding period to place her bid. The impact of sniping on the final price and parameters affecting the probability of sniping are examined in this paper. The empirical results for both auction web sites show that seller's feedback rating score has significant impact on the final price. The tests regarding sniping provided significant results only for the eBay auction. The effect of sniping on final price is not clear since we obtain different results for different specifications, but we found out that the experience of a bidder increases the probability of placing snipe bid. The study should be especially useful to all users of internet auction portals.