First off, howdy and welcome to the forum
Second, this may sound very blunt, but the answer is simple. If you are a new rider, don't buy a green horse, period. You need a horse that knows the ropes so that they can help you to learn. If both the horse and rider are learning at the same time, it almost always ends in frustration unless there is a trainer present every time you handle the horse.
With a green horse, every
little thing you do matters and it doesn't take but just one or two mistakes before you're in a whole heap of trouble; unmanageable horse, one or both of you hurt, make you scared of riding or handling horses, etc.