You probably know this, but you can usually tell by watching their legs. If you watch Liston's leg placement in the video with the hook you can see he had quite a bit of weight of it (if the cracking sound of it isn't convincing enough).
God I can't imagine being Liston- worked your way up Finally got a tile shot and then...........nobody wants you as champion. Further more what name fighter besides Ali was there around to even make money with? Then the Police are looking to arrest you every time you breathe and now being Champ your a high profile target.
8 years and he still quit on his stool on the 6th round in a tied fight? His mental strength is questionable if it took him that long to get his belt then he quits twice, wanting no part of Ali.
I never question the heart of most boxers unless I know for a fact. It took him 8 years to get a shot and when he won he was cast as the villain. Pretty sure that gets tiring after awhile.