In order to conduct a business responsibly, a company should be insured.
This helps protects the client, the inspector, and the business.

My Professional Association, OAHI, has guidelines for professional and general liability insurance.    Meticulous Inspections has the industry standard insurance in place for conducting home inspections.
As of 2013, the rules have changed with regards to Ontario regulations for workplace  health and safety insurance, including for home inspectors.
Meticulous inspections has chosen to follow the letter of the law under WSIB, which means registering and paying premiums on all income. I can provide a certificate for clients upon request. 
Other inspectors not doing so leave the door open for  a huge liability for their clients, if the (non-WSIB insured) inspector is injured while at a property. Under the law, the house is considered a workplace while being inspected.
When working on anything other than the (existing or potential) principal residence of the paying client, such as working for an agent, investor or builder, the client technically becomes the ‘employer’. See this page for information; excerpt below:
Q19. What about home inspectors?
Currently, home inspectors are classified in our Employer Classification Manual under Rate Group 704-02 CU 4499-001: Testing, Inspection, and Related Services. To be exempt from coverage, the home inspector must exclusively do home inspections on an existing private residence where they are paid by, and work directly for, the occupant or potential occupant (or member of their family). However, home inspection work is not exempt when it is for potential purchasers or a member of their family, who do not intend to occupy the residence themselves.”