Horse Veterinary Questions? Ask an Equine Vet.
I am sorry you are in this predicament and it is a commonly encountered one.
I have performed pre-purchase examinations on many horses and following discussion with many equine vets on the subject, the advice given to the examining vet is to fail the horses examination immediately if a sarcoid is present. Sarcoids are a mysterious tumour and they can behave erratically and treatment can be difficult. They are a potential can of worms that will leave you with a horse that is unable to be ridden or is very costly in terms of attempting to remove/improve the sarcoid.
If you are spending a lot of money on the horse, and albeit nothing in life is guaranteed, I would walk away and look for a horse that doesn't have any issues from the offing.
No problem! I hope it was of some help
Good luck with the search.