Ask any boxer, coach, expert, etc.; boxers fight through injuries all the time. It's part of the job. Nobody is ever at 100%, especially not veteran fighters in their mid-30s who've logged that many hours in the ring. Not fraud.
I can't imagine a rematch. It would be like any other Mayweather PPV from the past 2-3 years. It'd make less than the Canelo fight. At this point, Mayweather has earned the right to do whatever he wants as an athlete. As a person, not so much... But I couldn't criticize him for taking a couple of easy fights before retiring, as a kind of victory lap. IDK. If he wants to really make history, his best option would be to go for the 160lb championship, which is currently held by Cotto, a fighter he's already beaten.
As for Pacquiao being a sore loser... In the past, he's always been the epitome of the class act. Check out his postfight interviews after his loss to Bradley (one of the worst robberies in the history of title fights) and after the last Marquez fight. This one was weird and uncharacteristic. So... I'd probably let it slide and consider the pressure that he was under, national hero, etc.
That said, I can't agree with OGG re: the odds. What were they, really? 60-40? 70-30? Betting on Pacquiao wasn't that crazy. Sure, it was, in hindsight - 1 minute into the fight, it was obvious that the reach disadvantage, the lack of lateral offense, the very low punch output... Manny couldn't win with game plan. IDK. Anyway, people should never place bets large enough that, if they lost, they'd miss.