Obito and Orochimaru weren't truly that good of manipulators. Unfortunately for Orochimaru, he may have intelligence but that doesn't stop his ass from being off putting with his jutsu and movements.
People seemed to buy Obito's shit, but he was extremely suspicious. I think that either 1), others believed him for plot convenience or 2), it didn't really matter to them if Obito was who he said he was.