So many options.
Auctions are one of the largest requests for any new site that wants to sell to the masses. Most auctions sites are user based where the site relies on the user to post their listings. Others use auctions to privetely sell there goods. I have worked with both types. The most successful auction I wrote was a php / mysql based for sports memorabilia sites. Once recorded my software generated over 2 million in revenue during a one month auction. I first started working on auction based systems in 1997. I started working with auction systems when EveryAuction was popular. Back then, EveryAuction was a perl based application that used a flat file system to store it's data. In the early 2001 I created one of the very 1st PHP/MySQL auction system called RB Auction.