Reason:
Hufflepuff stole 2,000BTC from Primedice by cheating. They allowed his withdrawal and didn't stop any of his withdraw just because they didn't find any proof of hufflepuff cheating yet. Then finally they found how he was cheating but it was already too late. He had already withdrawn 2000 Bitcoins..
As any other site, Primedice allows you to verify bets. But the story of Hufflepuff is alone enough to prove that there is nothing shady going on at the server side as he was able to predict the next bet every time with 100% accuracy.
So this must be enough proof to show they aren't rigged and are very trusted in the Bitcoin community
they have provably fairplay there, as can see when rolling the slot, the verify system is just beside to you for verify 
