If a judgment has been set aside, must the bailiff return your money?

No

The creditor whom the bailiff was acting for must return your money.

The bailiff must return any fees he has taken from you,^[1] or if he refuses, then the debtor may apply for a fee assessment hearing^[2][3] together with an application for legal expenses.^[4]

^{[1] Regulation 17 of the Taking Control of Goods (Fees) Regulations 2014
[2] Regulation 16 of the Taking Control of Goods (Fees) Regulations 2014
[3] Civil Procedure Rule 84.16
[4] Civil Procedure Rule 46.5}