In his favor was the audience's insatiable demand for good gossip.
"Twitter in the transfer window does seem to go slightly insane," says Oliver Kay, a soccer writer at the Times.
Gardiner's tweets imitated the language of sports journalists and were focused at peak times, particularly evenings after Champions League matches.
Before tweeting a rumor, he would often send a teaser – "big news in 30 minutes". That added to his follower count, which he says peaked at about 25,000.
Gardiner interspersed his rumors with genuine titbits from newspapers to lend his Twitter account more authority.
In June, James McArthur, a soccer player with recently relegated Wigan Athletic, followed his account. That allowed Gardiner to contact him privately with an exploratory message: "Are the rumors true?"
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After a friendly exchange, Mr McArthur put Gardiner in touch with another Wigan player, Grant Holt. Gardiner spent Christmas eve in a private Twitter conversation with Mr Holt, then the subject of transfer rumors.
But Gardiner's best source remained his imagination.
As the January transfer window opened, Sam Rhodes tweeted that Mohamed Salah, "one of Europe's brightest prospects", was finalizing a £9 million ($14.8 million) move to Liverpool.
The claim was denied by Liverpool, but picked up by sports websites, including Al Jazeera's. Sam Rhodes was briefly among the most popular Twitter phrases in Egypt, Mr Salah's home country.
"I made this up in my living room!" exclaimed Gardiner, seeing his rumour echo online.
A Telegraph journalist, however, identified the account as fake, leading to its suspension.
"Almost every generation thinks that the current generation is less honest than their elders; it goes back to ancient Greece," says Jeffrey Hancock, a professor at Cornell University.
"I don't think people are lying more today. But with technology, when people chose to be dishonest they can do it at scale."
Gardiner, now 17, maintains his plan was never to make financial gain, but to build a platform for his passionate views on soccer, particularly Arsenal. "I did maybe feel a tiny bit of guilt, but not that much," he says.
He now wants to be a real journalist.