If you are an employee who sells goods or negotiates contracts for an employer you can deduct expenses like other employment expenses except your deduction generally can not exceed the amount you earned as commission. Or if you are a salesperson and your employer require you to pay expenses to earn your employment income, you can claim deductions for such expenses from your total income. CRA guide T4044 helps you to calculate the expenses you can deduct. It also gives you all the information you need to claim the employee goods and services tax/harmonized sales tax (GST/HST) rebate. To claim Employment Expenses your employer will have to complete and sign Form T2200, Declaration of Conditions of Employment.
If you have more than one employer, ask each employer to complete and sign a form. Depending upon the conditions numerated in T2200 you may deduct expenses, such as, Travelling, Parking, Supplies, Computers, Cell phones, and other office equipment, salaries of employees working full or part-time for you, proportionate expenses of your work space in your home.