I disagree with your premise. Lack of audio evidence doesn’t mean he’s lying. I’m not sure what should/shouldn’t be recorded. I’ve never worked as a camera guy, but I’d imagine that they are selective in what they record. I know they are selective in what they broadcast. I also don’t record Celtics games while I’m there so I haven’t caught anyone in the act. This is me attempting to answer your question.
Are the other men lying as well, because there’s no audio?
There's a distinction between the level of audio recording at the NBA Finals and just about any other day-to-day event. There entire area around the court is mic'd with ultra-sensitive microphones. I don't think you answered my question -- I don't see how anybody can not admit that the lack of evidence and Draymond's own response cut against his story -- but I'll answer your question anyway. (After noting that 1. Draymond has made these type of accusations before, saying it's happened in various arenas, again without evidence; and 2. Draymond himself uses racial slurs, including calling Perk a "c--n".)
Smart, Demarcus, and Michael Wilbon all said it happened to them.
These are three distinct incidents. Regarding Smart, I believe him about the Boston incident. As I recall, he said that he was in a car, and a woman and child were pedestrians, right? I'm not sure that he calmly rolled down his window and politely warned her to get out of the road, but I believe the gist of the story: there was a white woman with her kid, trying to cross traffic. A black man shouted to her, and she reacted with anger and racism. Why believe him? Because there's no evidence pushing back on his story. It's not a situation where you'd expect the interaction to be caught on tape. Similarly, if Marcus had reacted to the event at the time, telling the media that some angry woman told him "F" off, only to later five months later change it to "she called me the N-word", that would be questionable.
Incidentally, I do not believe that the reason Marcus went into the stands in OKC was because somebody called him a slur. I think that was an attempt to avoid consequences for losing his temper.
Wilbon I believe, or at least mostly believe. The only part of his story that doesn't seem believable to me is that the *only* place he's been called the N-word was in Boston Garden. As he said, he grew up during the civil rights area, in a city that was quite segregated. I'm shocked that any black man in America born in the 1950s has only been called the N-word once or twice. But the rest of it? I absolutely believe that he was called the N-word in Boston during the 1980s. I also believe him that he was warned not to walk in Southie. I've noted my own perception of South Boston in the early 2000s, mentioning its like there was an invisible marker for blacks that said "do not cross this line". So, again: the story makes sense, and there's no counter-evidence to suggest that it isn't true.
Boogie... I don't know. It got investigated. The team found that the kid (below 18) likely acted inappropriately, but that there was no evidence of a slur. Boogie says the slur was "muttered" or "mouthed".
The source said the fan sitting a few rows behind the Warriors’ bench was taunting Cousins during the game. At one point, the source said, Cousins saw the fan mouth the n-word at him and Warriors and TD Garden security were alerted.
The fan was removed from the arena, and the Celtics launched a multi-day investigation in which they interviewed fans who were sitting in that section and others in the bench area, and also reviewed all available video that could have shed light on the alleged incident.
No one corroborated Cousins’s claim. And while the video made it clear that the fan was speaking to Cousins during the game, the exact words were not clear. The source said that if there was any evidence that the fan had used racially charged language, or if any others in the area had corroborated Cousins’s story, a lifetime ban would have been implemented.
If Boogie "saw" the fan "mouth"ing the N-word at him, that's a good reason why others wouldn't have heard it. But there's also all kinds of room for misinterpretation there. So, I don't know. I do believe Boogie that he truly believes that's what happened; I don't think he's lying, but if this is lip-reading, I can see where somebody could confuse "N-word" with "F---er".