That horse doesn't have a bucking issue, it has a rider issue. Green horse + novice rider = spooking. Lets the trainer train him, which is good, and then puts him out to pasture, so he's probably forgotten a bit. Doesn't sound like a horse who is "known to buck". All horses buck when they are spooked, it's a natural reflex, especially when they have an unconfident green rider.
A horse with a "bucking issue" is a horse that bucks with malicious intent to unseat the rider under normal riding circumstances. It can be worked with by a skilled rider or trainer.
A green horse I would buy, a malicious horse I would not.