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Any tax advantage for registering a residential house as a business? (I want to apply legal pressure to my landlord)
To the best of my knowledge, in California there's no such thing as registering a place as a business. There's zoning (residential/commercial/mixed/etc), and there's "a business registered at a place". But there's no "place registered as a business". So you better clarify what it is that you think your landlord did. It may be that the place is used for short term rentals, in which case the landlord may have to have registered a business of short term rentals there, depending on the local municipal or county rules. Specifically regarding the deposit, however, there's a very clear treatment in the California law. The landlord must provide itemized receipt for the amounts out of the deposit that were used, and the prices should be reasonable and based on the actual charges by the actual vendors. If you didn't get such a receipt, or the amounts are bogus and unsubstantiated - you have protection under the CA law.