How can you prove that your goods don't belong to the debtor without receipts?

Receipts for purchase of goods is not a requirement for proving ownership of controlled goods.

If bailiff take control of goods that do not belong to the debtor, the owner makes a claim to controlled goods, and makes a witness statement setting out how the goods were acquired.^[1][2]

Bailiffs demand the receipts for goods are produced, even in circumstances he knows the goods may be antique, or heirlooms and getting a sales receipt is impossible.

It is to frustrate the debtor to compel him to pay the money, knowing the owner is not going to let go of his goods, whether it is actually legally theirs or hired. The bailiff usually doesn’t actually expect to obtain full legal rights over them.

^{[1] Civil Procedure Rule 85.4
[2] See Making a third-party claim to controlled goods}