They should have insurance to cover them in the event of a fire, theft, flood, etc. You should have general liability insurance to cover damages caused by your actions or inactions (bad repairs/failure to repair). General insurance also covers you if a tenant's guest slips on the stairs or gets bitten by a dog you allowed a tenant to keep. You might consider incorporating your business. This will protect your personal assets in the event the rental company gets sued for more than the assets are worth.
------------------
This is not legal advice and you are not my client. Double check everything with your own attorney and your state's laws.