Errors of fact are the strongest ground. Wrong square footage, a basement recorded as undeveloped when it is finished, a missing garage, an incorrect lot size or a bathroom not counted are all objectively checkable and all common. Send the correction with evidence, such as measurements, photographs, receipts or a permit number from the City of Saskatoon, rather than an assertion.
Better comparables are the second ground, and they have to be genuinely better. A sale closer in date, ideally within 90 days, closer in distance, closer in property type and closer in condition than the ones used is worth submitting. A higher priced sale that is simply a nicer house is not, and sending it weakens the rest of your submission. Listings that have not sold carry no weight at all.
The deeper issue is usually that the appraiser could not see what you know. Renovations completed without a permit appear in no record and in no online estimate, so an appraisal built largely on public data will understate a home that has quietly been improved. Joel Dyck's hand-reviewed valuation documents that work in a form a lender will actually read.