He recently started bucking and after ruling out pain/saddle fit I decided it came down to the flush of autumn growth in the pasture so I now need to lunge him to get the bucks out before riding and am upping his exercise.
See now that's something that concerns me too. Even if a seller is 100% honest, you could take a horse advertised 'no buck, no bolt, no drama' and end up with something that you have to lunge so it doesn't toss you.
Seems to me that basically, horse ownership is only for people who can handle, or who are prepared to deal with bucking, bolting, biting, etc - because even if you buy a horse not that way inclined, apparently something as simple as the grass they eat can change everything.
Personally, I'm backing way off horse purchasing at this point, and reconsidering riding too. I love riding, but it's just very difficult to get my head around the notion that a perfectly good horse could start picking up those undesirable, let's face it, life threatening behaviors. A buck or a bolt could easily kill a rider if they were unlucky.
Compare that, to say, a dog. (I know horses and dogs aren't the same thing remotely, but they're both powerful animals capable of doing great harm.) I'm 99.9999% sure that my dogs are never, ever going to turn on me and start biting me. That's because I've known them all their lives, have a bond with them and know their range of behavior. But a horse, because it's a prey animal and because they seem to be more 'primal' creatures in general, can apparently go from being one kind of animal to another in a way that other domesticated animals just don't.
Maybe this is getting blown of out proportion in my head, but the more I see other riders working with mounts which they claim to be good but which exhibit potentially lethal behaviors, the more I think that maybe horse people are just incredibly brave souls.