When it comes time to buy a horse it is not something that is done quickly. It takes a little bit of planning and doing some proper reviews and research. The first priority is knowing that there is going to be the proper housing available for the horse which should include a good pasture for the horse to run 
free in, as well as a barn with the stall where the horse can it be housed in bad weather.
It also comes with a certain amount of financial responsibility aside from the initial purchase. The costs involved may be having to board a horse at a proper facility if one is not owned. Then on top of this there is the feed and the health care that must be attended to.
Aside from finances there is time that must be put in to the horse to keep it happy and healthy. Buying from a reputable breeder is also another important factor that has to be taken into account when making the purchase.
Horses can have genetic defaults that can have dramatic effects on them as they begin to grow.