An Auction is a listing of an item for sale with a starting price (or minimum) where individuals have the opportunity to out-bid one another in competition for the purchase of the item, thereby driving the total sales price of the item(s) up.
In general though, provided a "bidding war" does not take place, Auctions tend to close for less than the retail prices at many new and used retail outlets.
A Bidding War is a highly competitive set of bids back and forth between two or more individuals, seeking to outbid and pay a higher price for the item(s) than their opponent(s) would be willing to pay for the item(s). Bidding Wars tend to benefit the seller(s) of the item(s) in that the price can sometimes be driven up to many times its actual market or retail value. Due to the open nature of an auction, bidding could go on indefinitely, which is one of the reasons why time limits are generally placed on auctions, so that a bidding war must eventually end.
- Craig's List: http://www.craigslist.org
- eBay: http://www.ebay.com | KiJiJi
- Amazon: http://www.amazon.com 
- PCI Auctions: http://www.pciauctions.com (restaurant/hotel/enterprise equipment auctions and liquidations)
- Garage Sale Rover: http://www.garagesalerover.com/ | iOS | ANDROID
- Yard Sale Treasure Map: http://www.yardsaletreasuremap.com/ | ANDROID
- Picker's Pal: http://www.pickerspal.com/ | iOS | ANDROID
- Garage Sales Tracker: http://www.garagesalestracker.com/ | iOS
- G-Salr: http://gsalr.com/
- Weekend Treasure: http://www.weekendtreasure.com/
- Shpock: http://shpock.com/en/
- WeBid - open source PHP Auctions script: http://sourceforge.net/projects/simpleauction/
- HotScripts - PHP Auction scripts: http://www.hotscripts.com/category/php/scripts-programs/auctions/
- Open Source Auction scripts: http://www.opensourcescripts.com/dir/php/auctions.html
- Writing your First Google Marketplace App using PHP: http://code.google.com/googleapps/marketplace/tutorial_php.html
- wikipedia: Auction
- How To Buy Anything From Japan (even from Yahoo! Japan Auctions) With FlutterScape: http://www.tofugu.com/2010/05/13/how-to-buy-anything-from-japan-with-flutterscape/
- Selling on Amazon: http://www.amazon.com/gp/help/customer/display.html?nodeId=1161232
- YardSale Treasure Map uses Craig's List as its source for all sale events: http://www.tucows.com/preview/610897