CRA requires that receipts be kept for all expenses claimed in the tax return.
There are differences in the expenses that self employed individuals, commission employees and other employees can claim.
Self employed individuals use the form T2125.
Commission employees and other employees use the form T777.
Commission employees such as car salesmen can claim tax return preparation fees as well as house insurance and property taxes when they have an office in their home.
Employees, other than commission employees, can only claim heat and hydro if they have an office in the house.