When searching for a competition horse, common mistakes lay in the misconception that a potential horse will fit the bill. If you have not yet had competition mileage / experience it is best to buy a horse that knows it’s job.
Take an experienced professional /trainer with you who understands your requirements and is able to help you stay safe, ask the right questions, and ultimately know that your capable of jumping, or hacking the horse in question to minimise risk.
A horse with jumping experience will generally be more forgiving and help get you out of trouble, than a green (younger/ less experienced) one.
Best see proof of experience, by affiliated results, facts, videos, than take a vendors word for it!