I also believe that normal season games could be rigged. But I don't presume this kind of things can happen on play-off games. I have been following NBA for years. There are too many unreasonable things happening on some matches.
Why not?
If I may ask, what do you think is the purpose why the NBA rig some games?
Regular season or playoffs is the same, if they proven rigging a single game, then we can assume that they will also do it with the other games.