I've only had lessons with two trainers. Both are very type A personalities. Both are borderline yelling just to get their voice to carry (And my ears don't work as well as they should), but the only issues I have are when they expect me to know something they've never shown me. Once, one told me to change rein, so I went and changed rein on a small circle, and she yelled at me that she meant down the diagonal. She said it in such a way that it made me feel stupid, and I never spoke another word for the lesson. I have anxiety issues and asthma, and as the lesson went on, it only got worse. I was being criticized every stride, and I tried to fix it but she never told me if I was doing it right, so I would try different things until she yelled at me- the only indicator I had. Eventually I had enough after riding a lap or two around the arena, unable to see through my tears and unable to breath. She was still criticizing me and wanting me to pick up a canter- something that freaks me out even on the best of days.
I don't mind being yelled at and criticized, but you need to tell me if I'm doing it right. My favorite instructer is one of my music director- she believes in giving at least one compliment for every 5 criticisms.