The horse with the White Tail: a Veterinarian's Tale

Dr. Knopf with a miniature horse foal

Over the Thanksgiving weekend Dr. Knopf showed me a text message that she received from a colleague, which (loosely quoted) said: 
"I performed a PPE [editor's note, pre-purchase exam] on two horses for buyer in TX.  I texted the buyer when complete.  Buyer asked about results of horse with white tail. [Insert mild expletive here], I never did a PPE on a horse with a white tail!"

The Backstory
The vet arrived at the barn and asked for the two horses being sold to the particular out-of-state buyer.  She was given two horses for the pre-purchase, though as was unfortunately discovered later, the vet was given only one correct horse and had not been given the "horse with the white tail."

Who will pay the vet for the PPE on the wrong horse? 
The buyer will understandably say she is only going to pay for the PPE for the horses she is buying. 
Whether it was the barn owner, a trainer, or a groom that got the horses out for the vet, that party will likely claim it wasn't his/ her fault, s/he wasn't given sufficiently clear information on the horse, or that s/he didn't have any responsibility to get the horses out, and most importantly, s/he will not be stuck with the vet bill. 
Without more facts it is difficult to know who is at fault, or at what percentage; perhaps the barn was responsible to provide the right horses, or the vet needed to get more information from the buyer ahead of time.

What if the wrong horse was sent to Texas?
This is surprisingly not uncommon- when the wrong horse is sent to a buyer's barn.  This is sometimes done deliberately, such as fraudulent buyers who intentionally misrepresent the horse being sold.  But more often this is done accidentally or negligently.  In general, the person who committed the wrong would pay for the transport of the horse to return it to the barn and would bear the risk of loss of the horse while it is in transport.  
Many international horse sale disputes have arisen when the buyer claims the wrong horse was sent, but the seller asserts that it sent the correct horse.  This issue has become increasingly common with Internet sales.

Preventative Steps: Oral and Written Communication!
Your Purchase and Sale Agreement must fully and adequately describe the horse to be sold (tattoos, brands, chips, distinctive markings).  This Agreement can be given to the vet for his/ her records prior to performing the PPE.  An added benefit is that the vet will understand from the Agreement the intended purpose of the horse or what guarantees have or have not been made.
At the very least, the buyer should clearly specify to the vet when ordering the PPE which horses are to be examined.  Finally, sending photos to your vet of the right horse can always be helpful, though be sure to capture in the photo a unique detail.... such as a white tail.