Fake letters have been presented on the forum before.
The issue is not whether wifi bandit is trustworthy. The issue is whether the letter is genuine. It's perfectly possible that a fake latter was sent to wifi bandit and he presented it in good faith.
I don't want to be rude but I think people who accept this letter as genuine display a lack of good judgment on this occasion.
More broadly, how can we determine if Watchtower documents are genuine these days? It's not an easy problem to resolve given new technology. Historians and journalists increasingly face these problems. The distinction between real and fake, reality and simulation will become increasingly blurred. Fake documents (and pictures and video) may pass for real, and real documents (and other media) may wrongly be dismissed as fake. It's a real(!) problem.