Some people feel they can get by without a bill of sale, but they could face issues without one. For example, you may create a payment plan with the buyer to ensure you get all the money. However, if you don’t have a bill of sale, you don’t have a binding contract. The buyer could stop the payments, but without a legal document, you can’t prove the buyer agreed to them. Because of this, you could wind up losing money without any proof to reclaim your horse.