Billy is a pretty good horseman and always rides finished horses and knows how to buy a well trained horse.
As a result he cuts a fine picture as he enters any arena and his friend is quite impressed with Billy skill as a horseman.
You got to know what you don't know!
This is an unfortunate reality in the horse world; there are so many people who have been around horses their entire lives, but does that mean you know how to train a horse? No.
I had a friend who went through this kind of thing when she bought a green gelding. Everyone had forewarned her that the horse had issues undersaddle, but her eyes were too caught up in the 'feeling' of love she had for the horse. Well when the horse started bucking her off, and refused to be saddled, she blamed the horse. She didn't realize that the horse's issues stemmed directly from her lack of experience to handle those moments when the horse needed confidence from his rider/handler. And when she did encounter issues, she tried to rush him through them, causing further confusion and chaos in the horse's mind.
By the time I went out one weekend to evaluate the horse, as she wanted some opinions on where to go with him, she couldn't even put the saddle pad on him before he was lunging, rearing, and bucking. I worked him from the ground, and got him moving out nicely in the round pen, listening to my cues, and when he was doing that well, I pulled out a bareback pad, and started desensitizing him to it...at first, he panicked, and started around the round pen again (I was working off lead). Rather than try to stop him, I pushed him to go faster, and did some swapping directions, then stopped him, and invited him back into the center of he pen. This time he stood as I rubbed him all over with the pad, and slung it over his back several times. I put it on, and tightened it. I then pushed him out of the center of the ring and asked him to move out...no bucking, rearing or nonsense at all came out of him. Brought him back in, and did the same with the saddle; by this time he didn't even bat an eye, and cocked a leg as I saddled him up. The next day I went out, did a bit of round pen work, and saddled him up without incident. I told his owner that she needed a trainer to help her with the horse, and that his problems were stemming from her own lack of confidence in him.
This owner never did seek out consistent help with the horse, and wound up selling him less than a year after she bought him. Just goes to show that years of experience simply riding horses, doesn't mean you will ever know how to properly train one.