Fact of the matter is: people who are regularly involved in transfers (club insiders or employees in agencies representing footballers)will not divulge details that they've been asked not to. Their reputations and jobs would be endangered if they routinely go on divulging details they have been asked to keep private as someone from inside the clubs would eventually catch up to a serial informer.
When the clubs or agencies themselves try to leak out news, their preferred medium would be journalists in the mainstream media as that is the quickest way to reach the largest audience. This would also help them maintain relationships with journalists who'd give them favourable coverage in return.
Yes, there will be a bunch of individuals (employees in travel agencies real estate agents etc) who would get to know about the transfers beforehand, but, they'd be able to provide information only on limited number of deals. Most first timers wouldn't have twitter reputations to be heard out by the masses and the chances of them getting to know about a second big deal is minimal. So, ultimately, most twitter ITKs (apart from journalists with insider track) are just attention-seekers who're bluffing, regurgitating rumours they heard from elsewhere or the ones who were lucky enough to get some bit of adhoc information before, but, have no permanent means to information.
