A big spread between the two usually means the assessment cycle has not caught up to a fast-moving segment of the market, or that the property carries features, a view, a finish level, a lot assembly, that a mass appraisal model applied across thousands of properties cannot price the way one determined buyer will.
In Saskatoon that shows up on a smaller scale in luxury and acreage sales near the river, where comparable sold data is thin and a City assessment built for typical houses struggles to capture what a single high-end buyer will pay for a specific property. The Board of Revision exists to correct assessment errors, not to explain a sale price.
Joel Dyck prices from actual comparable sales rather than the assessment roll whenever the two clearly disagree. Get your hand-reviewed valuation from Joel Dyck.