When I resigned as Ambassador to blow the whistle on UK/US complicity in torture and extraordinary rendition, I had a number of official documents I wished to leak to prove my story. They were offered to WikiLeaks through two friends, Andrew and Jonathan. WikiLeaks declined to publish them because they could not 100% verify them.
Their reasons were firstly that they were suspicious of me and whether I was a plant; British ambassadors are not given to resigning on principle. Secondly a few of the copies were my own original drafts of diplomatic communications I had sent, not the document as it printed out at the other end.
That is how scrupulous they are. I can vouch for the fact that their record for 100% accuracy is no fluke, it is safeguarded by extreme caution and careful checking.
In the end we launched the documents through mass blogger action on the web, on hundreds of independent sites simultaneously. You can still see them all for example on William Bowles excellent blog, and they are worth a read, even a decade on. I think over that decade I persuaded WikiLeaks I am genuine too!