Your better off having the buyers creating an account, and depoisiting funds into their balance, and then using that balance for the penny bids.
I dont see the point of having sellers sell the items because people will scam this left right and center.
madbid.co.uk doesnt have sellers selling, everything sold is from the company itself. Best to put things up for auction like 10btc or 50btc, the money generated will be much more.
That's exactly how it works for buyers.
We have several ways to reducing scamming the system
1) Feedback rating system
2) We hold commission from auctions 7 days after Seller has shipped item or buyer has indicated receipt of item
The site where there is only one seller (the website itself) is set up for bidders to lose in the long run, my site is not intended to be that way. I want to increase the probability of winning items by having multiple sellers and not just high end products. If you could spend 2 BTC's to get a used 5gig mp3 player, y the heck not? We are actually going to be changing the site soon so that sellers get 100% of all commission, the only fees will be to cash out but you could use your credits to bid on other auctions.