Many times, a landlord will lose focus when attempting to let an apartment. A landlord may be so desparate to rent a property that any tenant with cash is acceptable. Frankly, most of the landlords who get into these unacceptable situations regret their actions down the line when they lose other tenants or lose rental income due to a bad tenant. Landlords need to change their focus to be successful. Property ownership is a business and should be treated that way.
Landlords provide a service to tenants.
Landlords are not the tenant's business partner. Once the landlord gives in to one of these situations, the tenant will be likely to take advantage again in the future. When a tenant is late with rent, a five day notice should be promptly served. When a tenant violates a lease provision, a ten day notice should be promptly served. Landlords must take a fair but firm stance with tenants.