Mystery auction is a type of auction where bidders bid for boxes or envelopes containing unspecified or underspecified items, usually on the hope that the items will be humorous, interesting, or valuable.[33][34] In the early days of eBay's popularity, sellers began promoting boxes or packages of random and usually low-value items not worth selling by themselves.[35]
Reserve auction is an auction where the item for sale may not be sold if the final bid is not high enough to satisfy the seller; that is, the seller reserves the right to accept or reject the highest bid.[37] In these cases a set 'reserve' price known to the auctioneer, but not necessarily to the bidders, may have been set, below which the item may not be sold.[36] If the seller announces to the bidders the reserve price, it is a public reserve price auction.[39] In contrast, if the seller does not announce the reserve price before the sale but only after the sale, it is a secret reserve price auction.[40] The reserve price may be fixed or discretionary. In the latter case, the decision to accept a bid is deferred to the auctioneer, who may accept a bid that is marginally below it. A reserve auction is safer for the seller than a no-reserve auction as they are not required to accept a low bid, but this could result in a lower final price if less interest is generated in the sale.[37]
Silent auction is a variant of the English auction in which bids are written on a sheet of paper. At the predetermined end of the auction, the highest listed bidder wins the item.[43] This auction is often used in charity events, with many items auctioned simultaneously and "closed" at a common finish time.[43][44] The auction is "silent" in that there is no auctioneer selling individual items,[43] the bidders writing their bids on a bidding sheet often left on a table near the item.[45] At charity auctions, bid sheets usually have a fixed starting amount, predetermined bid increments, and a "guaranteed bid" amount which works the same as a "buy now" amount. Other variations of this type of auction may include sealed bids.[43] The highest bidder pays the price he or she submitted.[43]
It is important to have realistic expectations when attending a government car auction. While you can find some good bargains, you are not going to find a brand new BMW for $100.00. Government auctions sell both fleet cars and vehicles that have been impounded by government agencies. The conditions of these vehicles can range from great to not running. Set your expectations and budget realistically. 
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