I have to agree, respect is the first thing, trust comes with time. I had a friend who bought a paso from a riding stable, she rode, the owner rode it and our other friend rode it, I passed
well she gets him home and takes a couple of days to get to know him the usual then she saddles him up and bam he reared. This horse reared on her over and over, luckily we had a friend who works with horses and after a month of him helping her they have finally gotten to the point where he doesn't. Although she does take precautions every time she rides him.
I think when you buy a horse and say, its had all it's life at a stable and you bring them to more of a trail riding pasture kept place, it has to be an adjustment. I had a friend who bought a ex barrel horse, she is a really nice horse but the lady who bought her isn't going to be asking her to take off so to speak. That horse has become somewhat of a nightmare for my friend. The horse was used to a firm owner and this owner is a softie. She likes to go but this owner doesn't feel comfortable with that.
When I bought my mare she was broke for trailriding and that was her only job. Then she spent about 7yrs as a broodmare. The lady I bought her from said her grandfather always made sure that he broke his horses well. She has done awesome, her only flaw is she will try to avoid me catching her, its not the toughest try I've ever seen lol its actually not even a good try
Just like my friend who rides awesome but she is intimidated of trail riding. She is used to lesson horses, and when you go trail riding a lot of things can pop up.
Your horse needs your leadership for its new job.
I would try Monty Roberts joinup exercise. I like Clinton Anderson he breaks it down for the common man. Youtube has lots of videos. I change directions a lot when I lunge, I don't just send them around in circles since I'm lunging for respect and leadership not exercise. Just my opinion