I've done a few of the 
  "out-of-state"  purchases and had vet exams done . You have asked for 
  comments and advice and here's mine:
   
  Communicate with the vet. Don't 
  assume he knows everything or he will check everything. Tell him exactly what 
  you want and what you expect. Fax a list over for him so it is accessible and 
  he won't forget.
   
  Unless you tell the vet, he/she 
  will do a standard pre-purchase exam which is checking out the horse for the 
  discipline stated and giving you the information of his findings whether the 
  horse should do O.K. for the stated use. He will tell you what he finds and 
  you will make the final decision. Most vets will not look for the things that 
  I suggest because they are not "trained" to look for these subtle clues. 
  That's why it is important for you to communicate fully. Pre-purchases are not 
  a pass or fail.  I do tell the vet that not only am I paying for a 
  pre-purchase but I am paying for his opinion, as I am out of state and I can't 
  see the horse in person.
   
  Try to get a vet that is familiar 
  with endurance.
  (stay away from vets who do a lot 
  of QH types and western pleasure)
   
  Have him evaluate temperament and 
  manners. 
  Have the vet watch the horse under 
  saddle.
  Check hoofs for symmetry. Explain 
  that you don't want club feet or high/low hoofs.
  Check shoulders for symmetry and 
  evenness. (stand behind and above horse looking down to wither 
  area)
  Check hindquarters for even muscle 
  development.
  Check upper forelimbs for muscle 
  symmetry.
  Check to see if hip bones are even 
  (stand behind horse)
  Check 
  conformation.
  Special attention to: off set 
  cannons, tied in at knees, sickle hocks, pastern 
  length.
  Check to see if horse is balanced. 
  Is front end proportionately larger then the hind end, meaning that the horse 
  "pulls" himself along, instead of pushing.
  Have him check the shoes for signs 
  of uneven wear.
   
   
  See if you can arrange a person 
  (sometimes the vet will bring an assistant) to video the 
  exam.
  Insist that the radiographs be of 
  above average quality. (Yes, you have to say this)
  Tell the vet that your stated use 
  is 100 mile rides (even if you only want to do LD) because the vet, in the 
  back of his mind, will know that you plan to ride this horse hard and he will 
  be more thorough  and critical in his exam.
   
  Of the 6 horses that I have 
  had  vet checked , most vets "missed" important clues. One vet 
  (endurance vet) strongly suggested that I NOT buy the horse, and I didn't. One 
  vet had such bad radiographs that it was impossible to accurately see the 
  joints. One vet overlooked so many indicators that said the horse was in pain 
  and not using themselves properly (uneven muscle development).  I could 
  go on.
   
  Assuming you've asked the right 
  questions to the seller and your vet is thorough, you won't be surprised when 
  the horse is delivered to you. You will have a great horse and you will be 
  pleased. Good Luck.
   
  Lauren
   
  Lauren & Allan Horn
San Juan 
  Capistrano, CA