A standard auction lasts 60 seconds, whereas a fast auction lasts only 15 seconds, but features more aggressive bidders. Rare auctions feature items that are high in value and sometimes unique, meaning they can only be won once.
There are dozens of potential bidders, each with their own stats which determine their aggressiveness to bid on items, how long they'll wait between bids, how much Gil they're willing to spend on any item, and whether or not they will make a last ditch effort to win an auction.
Auctions will have their time briefly extended if a bid is placed in the last few seconds of an auction, leading to potential bidding wars over items. In addition, whenever a player places a bid, there's a chance to intimidate the other bidders into dropping out of future bids.
Some of the names and faces you'll see hanging around the Auction House include Brahne, Gippal, Shera, Gestahl, and Don Corneo, among others!