For an advertising slot bidding problem, let's say there are two slots and two bidders. If bidder A bids \$10 and bidder B bids \$8, bidder A will win the first slot and pays \$8.
How about bidder B?
He will win the second slot, but how much does he pay since there is no more second bid following his bid?
Does he win the second slot without paying anything? Since it's a second price auction?