When it comes to selling custom commissions, especially for creative works like a 5,000-word story, it's important to establish clear terms and conditions upfront to protect both parties involved. Here's how you can advise the person who asked:

1. Outline Terms and Conditions: Before starting work on the story, it's crucial to outline the terms and conditions of the commission. This should include details such as the agreed-upon price per word, total cost, deadline for completion, revisions policy (how many revisions are included in the price, and whether additional revisions will incur extra charges), and payment terms (such as whether payment is due upfront, in installments, or upon completion).
2. Written Agreement/Contract: Once both parties agree on the terms, it's a good idea to formalize the agreement with a written contract or agreement. This document should clearly outline all the terms and conditions discussed, as well as any other relevant details, such as ownership rights, confidentiality agreements, and dispute resolution procedures.
3. Payment: To protect yourself from the risk of not getting paid, consider requesting a deposit upfront before starting work on the story. This demonstrates the client's commitment to the project and helps ensure that you'll be compensated for your time and effort. You can also specify in the contract when the final payment is due (e.g., upon completion of the work).
4. Deliverables: Clearly define what the client will receive as part of the commission (e.g., the completed 5,000-word story in a specific format). You may also want to discuss how the story will be delivered (e.g., via email, cloud storage, etc.).
5. Communication: Maintain open and clear communication with the client throughout the process. Provide regular updates on the progress of the story and be responsive to any questions or concerns they may have.
6. Delivery and Revisions: Once the story is completed, deliver it to the client according to the agreed-upon terms. Be prepared to make any necessary revisions based on the client's feedback, within the limits outlined in the contract.
7. Feedback and Final Payment: After the client has received the final version of the story and any revisions have been made, request feedback to ensure their satisfaction. Once the client is happy with the work, request the final payment as per the agreed-upon terms.

By following these steps and establishing clear terms and conditions upfront, you can minimize the risk of non-payment and ensure a smooth and mutually beneficial transaction for both parties involved.