How he is right now: he's very sweet on the ground and loves people. He wants to be a lap pony (we've worked on being respectful of space.) His previous owner told me he'd had some issues with a lunge whip that she thought resulted from overenthusiastic, but not abusive, use by previous owners. Under saddle, he's fairly willing but there are some issues. He's not especially sensitive to leg and bit, but he overreacts to anything else (a tap of the rein on his shoulder, a touch with a whip, the sound of a whip against a saddle, etc.) He gets very anxious about canter departures and tends to charge through them and go straight to a gallop. He spooks easily and bolts when he does—the last instance of that had him running through the bit and every ounce of strength I had could not hold him back, slow him down, or even get his attention. That was after a few weeks of serious desensitization work, too.
As I mentioned, knowing or guessing one way or the other isn't going to massively affect how I work with him. My trainer is working with both of us to get back to the basics and help him relax, so we can establish a solid baseline of trust. But if there are any tell-tale signs that would point one way or the other, that would be good to know.