The terms, daily rent, length of stay and condition of the home at handover, are negotiated as part of the purchase agreement and confirmed in writing by the lawyers on both sides, at legal fees typically $800 to $1,500 per side, through the standard Law Society of Saskatchewan closing process.
A rent-back helps most when a seller's next home is not quite ready, whether that is a new build, renovations, or simply not having found the right property yet, and it avoids the cost and disruption of a short-term rental in between.
It works best as a planned part of the deal, negotiated before the offer is accepted, rather than a request made after the fact. Get your hand-reviewed valuation from Joel Dyck.