Unfortunately, this does not look to be worth of development on osclass
Hm. An Auction plugin would be great ( willing to have it, and even pay for a custom develop). Im sure other agree but maybe made in this way :
1. Users can post Auction only in a predefined category ( created from backend with this purpose )
2. Users can put : - starting price
- ending price
- bid increment sum ( a minimum sum which he can bid )
- auction time
and all the other default atrr form theme, or plugins.
3. This should be chargeable if the admin desires it ( os Pay )
4. This type of listing should be displayed only on Auction page, or separate slider on front page ( few great options for themes - ability to choose which listing categories is to be displayed front page / search page )
5. The user who publishes an auction should have the ability to award a winner.
From business type of view, I'm sure it will pay of the effort of developing such a plugin