Blazer Caravan nailed it. If you want to claim Oswald did not assassinate Kennedy, or that the moon landing was faked, or that Riggs threw the match, it's up to the claimaint to provide evidence. If some codger comes forward and says 45 years ago he/she was mopping floors in the White House and overheard Nixon and Neil Armstrong planning a fake moon landing to divert attention from the Vietnam War, frankly, I'd need a lot more than that to believe it was true. And so would any semi-responsible journalist.
The more you look at it the fishier this fish story looks. The match was viewed by millions and millions more watched re-broadcasts over the years. This includes numerous sports media who have covered hundreds of tennis matches, including those played by Riggs and King. In all these decades no one had any suspicion at all that the match was anything other than fairly won by King. No one saw anything amiss.
But we are supposed to believe that this individual was in the EXACT right place at the EXACT right time to be the only person to overhear this unlikely conversation?
I will also point out this was a $100,000 winner take all match. So IF Riggs owed $100,000 in gambling debts (I have no idea if that is true, but take it for the sake of argument), then winning the match was clearly in his interest and in the interest of those to whom he owed the money. In fact it would have made more sense to bribe King to throw the match.
Finally, motive. What earthly motive would these Mafia types have in seeing King win? It's not like they were great supporters of feminism or opportunity for female athletes, in fact, more likely the opposite.
What is saddest is that a supposedly flagship sports media like ESPN, instead of treating this like a story from the Onion, actually gave it credibility. Anything for a site-hit controversy, even something so transparently fraudulent.