It seems like a great deal — a Presto card preloaded with hundreds of dollars sold for a fraction of the price. But a deal that sounds too good to be true, often is.

Metrolinx is investigating after approximately 1,100 Presto cards were stolen from a third-party vendor on Dec. 27. The cards, valued at $20 each, might also be loaded up with money from stolen credit cards.

"They'll fill the value with ... $500 and say, 'I'm moving, I don't need this card anymore, I'll sell it to you for a reduced rate,'" Metrolinx spokesperson Anne Marie Aitkins told CBC Radio''s Metro Morning on Friday. "There's a lot of people in this process that get hurt. People are losing hundreds of dollars."

Metrolinx spokesperson Anne Marie Aitkins warns customers to buy Presto cards from authorized dealers only. (CBC Metro Morning)

She says the scammer then cancels the card and freezes the money, leaving the buyer in the lurch.

Metrolinx, an agency of the Ontario government that co-ordinates transportation in the GTHA, also blocks the stolen cards immediately, as each one has a unique number.

"We don't lose much money at all," explained Aitkins. "If it sounds like a good deal it's likely not. You're going to lose your money and the card is not going to work at all."

Some riders are skeptical

On a relatively quiet Friday morning at Union Station in downtown Toronto, transit users wave their cards in front of the green and silver Presto kiosks before getting on a train.

Metrolinx says some of the people selling bogus Presto cards will go to the station with you to prove there is money on the card, only to cancel it shortly after. (Radio-Canada)

Chris Chengelai, who says he works in "information security," says he is relatively certain he wouldn't be fooled by this type of scam.

"Whenever I buy something, I usually go on the official website and I purchase it from there," he told CBC Toronto. "I'd rather pay an extra 50 bucks and know ... I won't have any issues in the future."

Presto user Michael Urlocher is somewhat more blunt.

"I'm just not that stupid," he laughs. "Look, you just pay your way on transit and you don't look for scams."

'They're very bold'

Back in March, the agency started warning customers about stolen Presto card scams on websites like Craigslist and Kijiji … even Twitter.

It's easy for the seller to prove the card works. In fact, they will meet the buyer at a station and authenticate the card with the Presto machine onsite, Aitkins said.

"They're very bold," she said. "People are embarrassed, they're afraid they're going to be in trouble so they often don't tell us."

She warned that the cards stolen in December will likely show up online soon, and emphasized how important it is to buy from an authorized dealer.

Police have not released any further information regarding the theft. However, they said no one has been arrested.