VAT question

Please could someone confirm or deny that I've interpreted the following extract from the VAT guide correctly:

If you are a selling agent and the supply you are arranging on behalf of your principal is taxable, your supply of services to your principal in arranging that supply is standard-rated. However, if the supply you are arranging for your principal is exempt from VAT, your supply of services in arranging that supply may also be exempt.

Where it says "may also be exempt", does this mean that it's up to the agent to decide whether or not they charge VAT?

Thanks in advance