"There are specific ways that good deals come about," says Michael Craig, author of "The Best (And Worst) Business Deals of All Time." First, there may be a difference in information between a buyer and a seller. For example, the U.K. Daily Mail reports the case of a crystal jug sold at auction. The auctioneers described the piece as a 19th-century French claret jug and estimated the price at a couple hundred dollars, but a pair of discerning bidders recognized it as an extremely rare Islamic ewer. This difference in information saw the ewer go for £220,000, rather than the £5 million at which it was later appraised [source: U.K. Daily Mail].
That's a bargain. And imagine the steal if only one bidder, instead of two, had recognized the auctioneers' error. Information differential is how educated buyers pick up valuable Shaker furniture or Superman comic books for pennies at garage sales.
Another way bargains happen is through high-risk, high-reward investments. Think of the lottery. In hindsight, spending one dollar on a ticket worth a million is quite a bargain. Unfortunately, for every huge payoff in a high-risk investment, there are many more people who end up wasting their money.
Combining these two can lessen the risk. Maybe you're an artist, and you think you can predict the next Jackson Pollock. Or maybe, due to your tech expertise, you've spotted the next Google. This is partly what happened to Peter Thiel, who in 2004 spent half a million dollars on 5.2 percent of a little Internet startup. That startup was Facebook, and in 2010, Thiel was worth an estimated $1.4 billion [source: WIRED].
Finally, bargains happen when something of relatively small worth suddenly explodes into something of high worth. If you happen to be holding that particular piece of property at the time of ignition, you've got a bargain on your hands. This is sometimes known as the unknown frontier model, and it's how the United States -- after trying to buy New Orleans from the French -- ended up with most of the western part of the continent in the deal known as the Louisiana Purchase. The French simply never imagined that the untamed, landlocked plains would be worth anything.
In the 20th century, these frontiers were many, from technology to oil to bandwidth, and so too were the diamonds in the rough that were discovered through luck or skill. Keep reading to learn more about the 20th century's biggest bargains.