You can tell because they'll have a lifeless look in their eyes, like they just don't care about anything anymore. Breaking a horse's spirit is not the way to train them. They do it all the time in Spanishland and it makes me sick. You're not a true horseman if you have to beat a horse into submission.
You know, it's interesting how a horseman vs a "normal" person with little experience will veiw this subject.
My husband and I were on a walk one day, and three guys came riding by on their horses; I had seen these people from way off (you know, cause I'm a horse crazed woman, and can "smell" horses from a mile away)...well even from afar, I could tell there was no true partnership/horsemanship going on between these horse and riders.
The rider who was in front was on a big gelding who was SO tense, and his 'canter' if you want to even call it that, was more of that super "hot gaming horse" hop...you know how alot of gamers hop into the ring, instead of lope, or trot? His eyes were showing the sclera, ears back, sweaty, and he was very tense against the bit. Hubby thought it was cool...I was disgusted; he was like, well that's just not how you train...darn straight that's not how I will EVER train a horse...I want my horse to actually enjoy his time with me, not be 'controlled' by a heavy bit, and whatever other means it took to get that horse 'that' amped. Only one of the horses in that group showed relative relaxation, and even he wasn't that relaxed. It's times like that I wish I were on the trails with my mare, so I could ask them just how much their horse would be willing to do for them, without force... I've put my mare into some pretty weird situations, and have never had to do more than click to her after giving her a chance to realize I wasn't going to put her in danger, and she dove right in...