I have only had 2 horses in training. Geepers and Shaker.
Geepers was in training for like 4 months as a late 2yr old. And then again as a 4yr old and as a 5yr old. But I was trying to sell him. And I couldn't ride that horse. It just wasn't happening. Everytime I got on him I hit the ground. After 6 of 7 times you just kinda give up on it. When anyone other then you can get on the horse and w/t/c him around and have NO issues. As a 4&5yr old It wasn't so much a trainer as just someone riding him. First the college girl and then The lady at the barn.
Shaker fell in so bad that I had Mr.Trainer and his wife ride him. To see if it was me or him. It was him. They had all the same issues that I did.
I have had a few horses ridden by the lady at the barn Dillan when I had him. and Shock when he was at the barn. Just to get some trail miles on them. But most of the time I don't like other people on my horse.
Other then Dad. There are only 3 people I would let use my horse without me being there or ride them for a length of time. (other the the random friend that comes up to ride with me.) Are Spidey, His Mom and The lady at the barn.
I like to do the work on my own horses. If in a lesson I'm having a issue and the trainer gets on to prove a point/see if its rider or horse issue thats fine.
But I like to do the work . So I know how the horse is trained and know how the horses mind works, what makes them think and move and such.
Edit to add-
I have lost a lot of trust in sending my horse off for training. Or having someone train my horse without me being there. Just from watching other peoples horses and how they came back from it and stuff.
1.A lady that took lessons with Mr.trainer bought 2 horses really cheep. And one was really good and the other had some issues. The horse she sent to him was younge healthy and sound and very fat and out of shape. He worked her SO hard that after a week she was dead lame. Brusied all 4 feet from the insanely hard ground in his arena. This came form Owner and Farrier.
2.Moons ago before I bought my Paint mare. Her owner had a "wp trainer" work with the mare. As she was a NICE wp horse but had been off work for around 2 years while she was bred and had a baby. Said "trainer" beat the living snot out of the mare every day and tied her nose to her chest and ran her around the round pen untill she was about to drop dead and THEN rode her for a hour. Owner took her to a hunter pace and didn't longe her before she rode her (couldnt no round pen and he never tought her how to go on a lounge line.) So she got on her. Before her but hit the saddle she was bucking. Bucked owner off and sent her to the ER with a shattered wrist and 2 fingers.
Said horse sat out in the pasture for a few more months.
Then I talked to the owner and cleaned stalls in the barn to pay for the horse w/ A little help from my dad.
I bought her rehabed her mind. It took a loooonnnggg time but she came around. I never had any issues with her. But she was very uneasy with adults riding her. Any kid/teenager could get on her even if they didn't know what on earth they were doing.
When I sold her (not my choice) She went to a home with 3 girls 6,8 and 11. She was happy with them to.