- The horse's age?
- What it has been used for?
- Its experience and training?
- Its health and soundness (does it have any physical limitations)?
- How long has it been ridden/driven (sometimes horses aren't trained until late in life)?
- Does it have any vices (bad habits)?
- Is it afraid of getting on a trailer, or of cars, bikes, cattle, mailboxes and other scary things?
After the horse has been put through all of its paces and you are assured it can do everything you want a horse to do, you may want to ask your 'second opinion' to try it. If they refuse that's a good sign you might want to thank the owner for their time and leave.
However if your adviser gets off the horse or out of the cart with a smile on their face it's finally your turn. Put the horse through all the paces you are able to. Decide how confident you feel. Does the horse respond well? Is it comfortable to ride? Does it stand still when you ask it to halt? Take your time making these decisions.