9. What if I sign a 'Form 4' with an agent who shows me a flat, and later, someone related to me (e.g. my spouse) buys the flat through another agent or directly from the vendor?

9. What if I sign a 'Form 4' with an agent who shows me a flat, and later, someone related to me (e.g. my spouse) buys the flat through another agent or directly from the vendor?

You may still have to pay the first agent commission. See Schedule 3 - Commission to be paid by Purchaser in your estate agency agreement ("Form 4"). If you are not sure, ask your solicitor.