The buyer has no right of entry without the landlord present also. How would the tenant know it's the buyer and not someone else. Proper notice to enter does not garantee entry, the tenant still has the right to refuse. The landlord issuing a 30 day notice to vacate would be viewed as retaliation because the tenant refused entry. The correct and legal reaction would be to issue a 'notice to cure' and only if the tenant still refused entry should the landlord move for termination of the lease. Simple lease violations do not rise to the level that a 30 day notice to end lease would be appropiate. But then, some landlords over react without thinking it through.