If it's the same Randy Byers I've run into (a real nice guy, graying goatee beard, does clinics, is a Josh/John Lyons certified trainer) then he's a ****ed good trainer.
If it's the same person, I would tend to chalk up any bad reviews to someone who didn't follow through with or didn't learn to follow through and reinforce/maintain what the trainer taught the person to do with their horse. Then there's the cases where other trainers try to drum up business by casting aspersions on their competition. Who was it, Joseph Campbell who said, "It's not nice to do to well"?
I wouldn't let one bad review affect any decision. If you like the trainer and he does good work, then hang onto that trainer or go with him.