The conspiracy theories sometimes fun to read/watch about, but I can't seriously consider them when there are no real proofs. In my opinion, there's too much money involved, hundreds of millions USD, in advertising during NBA games to risk losing it by trying to rig the games.
Yes so far there's no still an evidence about their claim about the rigged games of the NBA I also don't think they will let it happen since if the community knows that it was rigged I don't think any people will be interested anymore on this game.
I think it's hard to rig this game since you see players playing on the basketball court. You may be suspicious about referred acting erratically favoring some teams , or a star player no playing well in favor of their opponent, etc., but it is hard to justify this because sometimes it can be human error.