What are your goals in riding?
Do you want to compete? Which disciplines?
Where do you see yourself riding in 2 years? 10 years?
These are all questions to ask yourself. Then look at the horses who are doing these things (ie competing in 3'6" hunters, doing third level dressage, etc..) and then take an honest look at the horse you are looking to buy. Look to see if he is capable of taking you to where you want to be in the next 2-5 years, and then, at that point will he be able to be sold to finance your next horse (ie will he be too old, have lameness issues, have any vices like cribbing, etc..).
If your goals are to have fun and ride for fun - then any horse you feel safe on and who has no health problems is probably the perfect horse.
They say money doesn't buy happiness -- well happiness doesn't buy horses!