(FORTUNE Small Business) – They lurk outside every sporting event and concert in America: "Psst. Anyone need two tickets?" Scalping might just be the second-oldest profession. No one enjoys playing on this forgery-fraught black market, and ticket brokers' eye-popping markups aren't any better, but if you're a season ticket holder who can't make every game or a salesperson desperate to impress a client with sold-out seats, what choice do you have? Legitimate options are increasingly becoming available as startups Tickets.com, LiquidSeats, Ticket Innovations, and even category patriarch Ticketmaster have recognized the problem and are creating team-sanctioned online marketplaces for reselling season tickets. The services guarantee a ticket's authenticity and, unlike buying tickets on eBay, facilitate the exchange without contact between buyer and seller. Jeff Fluhr, CEO of LiquidSeats, estimates that $10 billion to $12 billion changes hands each year in the U.S. "secondary" ticket market. "There's no need to touch and feel a ticket before buying," he says, "so the Internet is perfect for this." Trials with teams like the National Hockey League's Blue Jackets and Major League Baseball's Mariners have been successful, leading to expansion to a number of other sports teams; the concept is set to spread to concerts and other arena events. It's too soon to know how big the trend will grow, but it makes implicit sense (the chart below explains how it works). Save me one on the aisle for the Redskins' home opener. --Julie Sloane

TICKETMASTER

WORKS WITH Columbus Blue Jackets, Phoenix Suns, San Antonio Spurs, Penn State Football

RESELLS WHAT? Season tickets of participating teams. Concerts and arena events coming soon.

LOGISTICS Bar code on old ticket is invalidated. Buyer immediately receives a new, printable ticket by e-mail.

LIQUIDSEATS

WORKS WITH Arizona Diamondbacks, Seattle Mariners and Sonics, L.A. Clippers, SportingNews.com

RESELLS WHAT? Season tickets of participating teams; other select big-name sports, music, and arts tickets

LOGISTICS Physical ticket exchanged by FedEx or courier, or reprinted and held at the venue.