Seller: He’s never done that before.
Buyer: Thank you for your time.
My horse shopping adventures continue. Why is it that the only horse trainer who has shown ongoing enthusiasm for my horse hunt is involved with a breed that isn’t popular for jumping? I refer of course to the saddleseat lady. If I had been absorbed by the collective and had decided to go three-gaited, I’d have a horse by now. Or, I certainly would have looked at dozens in the last few months. Unfortunately, I still want to jump. At least, I think I like jumping. It’s been a while.
What red flags have you encountered, with horses or in life?
Virtual Brush Box 
When I was in the market, I’d watch the demo ride. When the rider had shown me everything he/she wanted me to see, I’d ask to see the horse canter on a loose rein. Floating rein. If the horse didn’t canter reasonably politely without contact, I left.
For me, I ask for every issue because I can handle some issues, I just want to be aware of them. And yes, you would already have one of “these” horses if you were in the market! I know exactly where to look and who to talk to and who not to.
Possible red flags: game, lazy, needs a go forward rider, soft back (means low), needs vet care, it’s name is Streak(personal experience), Satan, Diablo, Devil, etc…
Other red flag is always “needs an experienced rider”. Usually translates to “slightly west of insane”. Other one is “jumper potential” in a horse over 6 years old. Means they’re looney to the point of unrideable.