A good guide knows the personality of each horse. Horses have their own buddies and can take dislike to another horse. Horses have a definite pecking order with a boss horse and varying degrees of submissiveness. The guide should know the bully, the mellow and the timid horses, and correctly line them up for the ride. These horses are trained to handle, the hazards of the trail.
Most dude string horses have a sound disposition and are relatively free from vices.
However, some dude horses have distinct personalities and know many techniques to avoid work. They can get bored with the hourly routine, their attention span lags and they look for something to liven up the ride, such as biting the horse ahead of them when no one is looking. Or purposely stalling and taking an unscheduled break on the trail so other horses can't get around them. When that happens the dude string more closely resembles a freeway traffic jam than a trail ride. Dude string horses work from dawn to dusk, carrying riders of all ages and varying levels of abilities.