As a property agent of Reality Agency, the only income is the basic salary and the commission. Total income is subject to the Hong Kong Salaries Tax. All personal expenses and outgoings, e.g. travel expenses, personal expenses are not tax dedutiable.
For expenses to be deductiable for tax purposes, it must be incurred wholly, exclusively and necessarily for the production of the income related thereof.
If the agent is an employee of a company, he can put all direct expenses in the salary tax return together with your argument that these expenses are deductiable for generating the salary incoem thereof.
If the agent is the sole proprietor of a firm which has made a commercial contract with the 'employer', then it is trading as an estate agent. The commission received will then be regarded as the income of the firm and all direct expenses will then be claimed as deductiable businese expenses.