Legal status is the step buyers skip most often. The City of Saskatoon can confirm whether a secondary suite was permitted and inspected, and a suite without that history may not be insurable or mortgageable as income-producing, even if a tenant has lived there for years.
The inspection needs to cover shared systems as well as each unit. Furnace, electrical panel capacity and roof condition affect both households, so a $400 to $600 home inspection on a two-family should flag whether those shared systems were sized for one household or two.
Joel Dyck reviews two-family purchases with this checklist before an offer goes in. Get your hand-reviewed valuation from Joel Dyck.