I'm Lucy, and I'd be happy to answer your questions today. I'm sorry to hear that this happened.
Tennessee law requires the landlord to notify the tenant of their right to do an inspection, and then the two of you are supposed to go through the apartment together. The landlord isn't allowed to keep the deposit for any damages not discussed during that inspection, Tenn. Code, Section 66-28-301. If they didn't tell you that you could request an inspection, they forfeit the deposit. They have to return the whole thing before they can seek any other damages from you.
A tenant that violates the pet policy does not forfeit his security deposit. The landlord's recourse is to evict the tenant for breach of the lease. They can only keep the deposit if the pet caused damage - but only if they notified you of your right to inspection and then gave you an itemized list of damages. If you sue for a refund of the deposit, you will win.
Ordinarily, the landlord can countersue, even though they broke the law. However, in this case, since they didn't notice the damage within 30 days, they can't collect any money for those "damages". They could only win a countersuit if you owed rent when you left.
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