DEFINITELY need to check that horse out thoroughly before you trade for it. The fact that he told you it was just the bigger pasture makes me wonder about the trainer. I know that often a horse reaches a point in their training where they decide,"I've done this, and I don't want to do it again" and they rebel a bit, but that sounds like way more than the normal don't wannas. This just occurred to me, do you have white clover in your field? Its not blooming here yet, and I am not sure where you are, but if so it ALWAYS makes them drool. Last year Jack dropped a gallon of spit on my hand when he came in from the field,lol.