Start of Sale Agreement
A pet sale agreement can be a simple one-page document starting with names, addresses and contract details of the pet's seller and buyer. You can write name of one party and their other details on top one side of the page and name and details of other on other top side of the page.
In the next paragraph, no matter in what format it is, you can give the pet's details. For example, if it is a cat, you can mention its species, colour, weight, sex, registration number and how long the animal has been in your possession etc. This can include all other details you may want to add in agreement with the buying party.
Confirmation of Sale
In a paragraph you can confirm sale agreement between the two parties, mentioning date and place of the sale and purchase. You may also mention name of any witness present at the time.
Terms and Conditions
Also, briefly mention terms and conditions of the sale agreement. This may include payment mode, delivery of animal and collection of any other belongings. For example, cage of a pet if it is a bird.
At the end leave a space on bottom left and right side of the page so that both parties can sign the agreement after accepting it.