Here is my advice from what I have learned.
1. Stay there as long as you need too! The owner shouldn't mind if she knows your coming to try out a horse. Also, don't choose on the first day. Come back again, and again until you're 100% sure. Don't get excited and just say you want this horse on the first visit.
2. Yes, bring your own tack, that way you can see how the horse reacts to your tack. Why not?
3. Of course smile? If you get nervous about how your face looks and if your smiling or not, you may make the horse nervous
4. If I was selling my horses, I would ask the person i'm selling too all kinds of questions, because I do care where my horse goes. It just depends on how she feels about her horses. I have met people come and think they are all that when I was selling one of my horses who meant the world to me. He did not
get to take him home that day.
5. If the horse is tacked up the first day, I would say ok? But come back, after you have looked the first time and ask if you can tack the horse yourself the second and third time. Horse selling industry is a screwy deal
gotta keep your eyes open
6. ASK ALL THE QUESTIONS YOU WANT! YOU ARE THE BUYER!