If he doesnt already know, you arent going to be able to teach him. (or her) and they will probably get offended. They are the professional. You can point things out and ask questions but there is a fine line if you want them to show back up and work for you IME.
Show us pictures immediately after a fresh trim for more feedback on the skill of the farrier.
I can tell you from experience telling a farrier how to do their job doesn't. Go over to well.
If he leaves toes long and heels under run chances are he doesn't have a clue and you telling him how to trim. Won't go over very good he will leave and never come back. I see your from mn seems like finding a good farrier is hard to do. All the ones iv used aren't good if there are good ones they won't come out iam too far away.
Called several no not in my range don't go that far north or no not willing to travel that far for 3 horses.
The first thing that caught my eye were all those wavy horizontal lines. They should not be wavy in any way.
Sometimes you just have to act dumb. Ask him why those lines are all wavy and what causes it.
Then say your were reading, and came across something that said that a hoof angle should be in line with the pastern angle, and if he can better explain it to you and show you what that means, and how to see it.
You may kill 2 birds with 1 stone this way. Pumping up his ego, and getting him to think about what he's showing you.....or teaching you, LOL