Give the participants a few hundred British Pounds; let them loose in an estate sell or flea market; and let them bring the "bargains" they find to auction. The "winners" get to keep any profit they make on the auction.
I've looked in on BBC America's broadcast of this show several times, but I haven't seen a winner yet. Every team always overpays for some piece of ceramic, wooden, or silver piece of junk and then finds themselves utterly stunned when they try to resell their bargain at an auction that usually gathers from 33 to 55 percent less than their purchase price.
The lasting message from this show is that the people in flea markets unloading their junk on the general public know what they're doing and will never get the bad side of any haggling they do with their suckers, er, uh, customers.