Get the permit record for the property directly from the City of Saskatoon before you assume any extra unit is legal, since a finished basement or converted space with no permit on file will not count toward your mortgage qualification no matter how good it looks in photos.
If the unit is legal and has an existing tenant, ask for the lease and payment history, since that documentation carries more weight with a lender than a listing's stated rental estimate. Canada Mortgage and Housing Corporation and most lenders apply specific limits on how much of that income counts, so confirm the exact figure with your lender before you finalize an offer.
A home inspection, typically $400 to $600, should still cover every unit before you close. Get your hand-reviewed valuation from Joel Dyck.