Law Number 5 of 1960 concerning the Basic Agrarian Principles Article 5 states that customary law in the context of land sale and purchase adheres to the principles of clarity and cash payment. Therefore, the drafting of a land sale and purchase deed is not mandatory to require full payment as long as both parties agree. However, this often leads to legal issues later, including cases where the seller commits a breach of contract (default). For this reason, the author conducted this study with the following research questions: 1. What are the legal consequences of the sale and purchase deed concerning default in land sale and purchase transactions carried out by the buyer? 2. How is the legal protection for the seller in the event of a default in a land sale and purchase transaction? The theories used to address these research questions are, first, the theory of agreements, and second, the theory of legal protection. This study employs normative legal research. The research approaches used include a legislative approach and a case approach. The legal material collection technique involves identifying and inventorying positive legal regulations, books, journals, and other legal material sources. Legal material analysis techniques are conducted through grammatical interpretation and legal construction methods. The research findings indicate that land sale and purchase transactions under the principles of clarity and cash payment allow for the drafting of sale and purchase deeds even though the transaction has not been fully paid by the buyer. This creates an opportunity for the seller to commit a breach of contract in such transactions, revealing a lack of preventive legal protection for the buyer. The legal consequence of the sale and purchase deed is that it lacks legal force if it can be proven that a breach of contract occurred during its drafting.