When looking at a horse you're considering buying, keep the following in mind in terms of the purpose/discipline for which you are purchasing it

• Soundness
• Any blemishes
• Movement
• Conformation
• Manners
• Health (history and current)
• Training and show history
• Size (and is it full grown?)
• Quality/flash - is the horse eye catching? will it stand out in the show ring?
• Pedigree (if considering breeding)

Be sure to keep safety in mind at all times - a timid rider probably shouldn't be paired with a timid horse.