What can a buyer do if the seller's tenant is secretly subletting the unit on Airbnb before closing?

An unauthorized short-term rental sublet discovered before closing raises two separate concerns: it likely breaches the terms of the existing tenancy, since subletting generally requires the landlord's consent under the Residential Tenancies Act, 2006, and it may also expose the property to municipal short-term rental bylaw issues if the municipality regulates that kind of use and the arrangement is not compliant with it.

Because this is a legal issue connected to the current tenancy, it is properly the seller's responsibility, as landlord at the time, to address before closing wherever possible, rather than something a buyer should assume will simply stop once ownership changes. Raise this with the seller and your own lawyer as soon as it is discovered, since it affects both the tenancy situation you would be inheriting and whether there is a broader bylaw compliance problem attached to the property itself. Understanding the full picture before closing helps you decide whether to proceed, negotiate, or require the issue be resolved first.