Hi Anonymous, thanks for writing to us on AskGuru.
You may refer to our agent directory here to find a list of agents who specialise in retail shop leases: https://www.propertyguru.com.sg/property-agent-directory
The market practice is usually 10% of the takeover fee or one month's rental, whichever is higher. However, you can negotiate with the agent who's handling the deal on how much to pay.
Hope this answers your question.