Since the how not to sell a goat days, I've made a few decisions, mostly based on good business practices when entering into a buyer/seller contract.
Anyone who buys animals from me now signs a general bill of sale that is short, sweet and to the point- name address and phone of both parties, ID of the animal in question and a statement of general good health of the animal(s) being purchased. A statement of no garantees, real or implied, that the animal will preform as it did at my farm is included since there are so many factors once the animal leaves my premises that I have no control over. If the person wants testing of any sort, the test results noted in the text.
This protects both parties in case of any misunderstandings, or foolishness on the part of the buyer.
There are two copies, each person signs one, and the signature of a witness is included, then each person has a copy for their own files.
That's about it.