i do a little bit of riding for a pre-trainer 2ish days a week, all the ones we get come straight from the breaker usually, they tie up, stand in the wash bay, walk trot and canter in a straight line and generally speaking have good manners.
i havent ridden many but we did have one that was broken in and then spelled, she has been more difficult than the ones who came straight from the pre-trainer
i guess they get exposed to heaps during pre-training depending on where they are, and im pretty sure (not certain) it is the pre-trainer who teaches them how to run, work into the bridle etc.
all of ours have been darlings (with a couple of exceptions of course

), but i think that is the environment they are in where i ride and how they are treated and what not.