We've all heard the rumors. If you dress up and tell a compelling story—maybe you're leaving for your honeymoon or heading to a funeral—you might finagle a free first class upgrade. But there's a problem: upgrades rarely happen. Years ago, it might have been possible, back when airlines struggled to sell those cushy seats up front. With an improved economy, however, many travelers have been buying first and business class seats, leaving fewer for upgrades. Even if airline employees wanted to make your day, they don't have much inventory to work with.

"There is no way to sweet talk or dress yourself up into an upgrade," says Jaime Fraser, a Virgin Atlantic spokeswoman. "If our airport staff are looking to upgrade passengers on the day of departure, there is a process that they follow which generally sees passengers that are frequent fliers of the airline—or those that have paid for a fully flexible ticket—benefiting."

On Virgin Atlantic, as at most airlines, upgrades into unsold seats tend to go to an airline's most loyal passengers, people who spend thousands of dollars each year on the most expensive tickets. A few years ago, these elite fliers could often count on freebies, especially when traveling within the United States. But now, even many of them must wait until the last-minute before they get the call to first class—if they receive it at all.

That's not to say that trying to game the system is completely hopeless. Millions of Americans fly every month, and while it is becoming increasingly rare, plenty of passengers fly in first class without paying for it.

Here are some strategies for scoring a free upgrade.