I am a Chartered Accountant and there is no such thing as "ligit telemarketers that work under Revenue Canada".
CRA does not authorize any body, even Chartered Accounting firms, to call people for anything such as audits or tax reviews.

The only time Revenue Canada will contact you is when they want to verify your claims on your tax return such as tuition fees, medical expenses, child care expenses and the like.    And they will send you an official letter via Canada Post, not by phone calls nor by e-mails.