Hi,
I think
http://www.thefactory.ro/joomla-forum/auction-factory/how-approve-bin-bid-6189.0.html.htmlanswers this question too.
As for the admin payment you can edit the template and simply replace the auctioneer's bussines email with the administrators.
There also can be created a pricing plugin for auction payments but this needs a bit more coding then a simple tweak. The advantages would be that payments will be integrated in the site Payment Interface : you can see / accept pay logs, available payment gateways will be used instead of only paypal, etc.
Sorin