The Vickrey Auction is held to be superior to the normal "high bid gets it"
auction. The difference in mechanism is that in a Vickrey Auction, the high
bidder wins, but only pays the amount of the highest unsuccessful bid (think
of it as winning with <losing bid+epsilon>).
If one has multiple units to auction off, the auction generalizes: the N
highest bids each get a unit, and pay the price of the (N+1)th highest bid.
Now, is there any difference (when N clears the market) between this price and
the classical supply-demand price?
These models imply that there are theoretical, as well as practical, reasons
for fixed-price transactions to be common.