If the tenant is on a fixed term agreement, the property manager/owner cannot make them leave because they decide to sell. The tenant can stay until the end of their fixed term, and the new owner will become their property owner. Sometimes a property manager/owner will negotiate with a tenant to end the agreement early and offer some form of compensation.
If the tenant is on a periodic agreement, and the purchaser does not want to continue renting the property (i.e. they want vacant possession of the property), the property manager/owner must give the tenant a Notice to leave (Form 12) or Notice to leave (Form R12) for rooming accommodation, that must allow at least 4 weeks’ notice after the contract of sale is signed.