Is my horse dead broke [[experienced horse people]]

I'm looking into buying this really nice Standardbred mare, 11 years old, supposedly a very nice ride. She's a trail horse, and when I go to ride her, to test her out and see if I like her, what should I do to see if she is dead-broke, safe, and dependable? I'm already planning on riding her at a walk, trot, and canter both bareback and with saddle on, giving her a bath, cleaning out her feet, grooming her, catching her and leading her around, tacking her up, etc, to see if she has any quirks or bad habits. I'm a good rider, but I need a horse to teach me everything, because I have gaping holes in my equine education. So, suggestions??

I prefer to take a friend with me to look at an animal and bring that friends horse along.

The reason being, you will see another 'side' at time when horses are around strange animals.

This last mule I bought out of state, I took a friend and his mule and we put the sale mule through the ringer. I wanted her for trailriding so when we got there, we went on a trailride with her. It was my friend, me on the sale mule and the seller on her horse.

My friend rode his mule close to the sale mule to see how she would react. Then my friend and the seller stayed back and we left down the trail to make sure she would actually leave the herd. As we got out of sight, I had them lope past me to see exactly what her reaction would be incase of an emergency. We went over trees, out of sight, left the horses, trotted off (she doesn't lope lol), but did anything and everything I could think of with her. Grabbed a slicker and put it on while on her. She passed with flying colors and I knew what I was getting with no doubts.