Tourists are flocking to the newly opened 9/11 Memorial at Ground Zero in New York City, but some are finding that their “free” tickets to view the site are not so free after all.

While most of the Memorial’s tickets had been booked and distributed for months prior to the opening, roughly 10 percent of the total number of tickets were reserved for distribution to local transportation and tourism companies. The Memorial board had hoped that this move would decrease traffic congestion around the site, as patrons opted for tickets with these services and used the variety of mass transportation options, like water taxi or bus, offered by them.

But it seems that at least some of these companies saw the gift of free tickets as an opportunity to hike prices. The New York Times reported that two well-known tour providers in the city, Big Taxi Tours and Gray Line, each boosted the cost to ride if 9/11 Memorial tickets were added in the package.

Big Taxi Tours, running yellow double-decker buses around the city, had customarily charged riders $32.50 for a regular tour ticket, but it recently upped the price to $37.50 when that tour included a 9/11 Memorial ticket. Once the Memorial board was aware of the price difference, it withheld further tickets from Big Taxi Tours until the company reset its prices. However, prices did not exactly return to normal following this discovery. Instead, the company decided to increase the cost of its regular tour to $35, charging the same fee for tours including Memorial tickets.

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Gray Line was charging a full $10 more per person on tours that included tickets to the Memorial, up to $49 from the regular fee of $39 for a regular tour of downtown. When confronted, the company claimed that it had anticipated needing an extra tour guide to accompany tourists on these trips, but it subsequently lowered the price to $44 per person. Urban blog site Gothamist.com was able to contact a former Gray Line tour guide who stated that he had never worked with a second guide for any tour. “In my ten years at Gray Line,” the ex-employee noted, “not once — not once — did I ever see more than one tour guide on a Gray Line bus.”

The company defends its decision to charge an extra $5 for a ticket-included package, claiming that the $39 fee is exclusive to the internet and these Memorial-related trips cannot be booked online.

Opportunism in the “free ticket market” is nothing new. In 2008, free tickets to Bon Jovi’s Central Park concert in New York City ended up for sale at a number of online auction sites, ranging in price from $0.99 to over $1,000. And the practice is not restricted to ticket sales. This past April, a number of London hotel owners accused London’s Olympic Organizing Committee with allowing preferential-rate rooms they had provided for the 2012 Summer Games to be sold by third parties in high-end package deals.