Three Years' Renovation Left for Landlord; He Denied $6000 Deposit, Regretted It

I rented for three years, and at my own expense I turned my landlord's bare-shell unit in a run-down low-income neighborhood into a bright, luxurious princess apartment. When it came time to move out, I told the landlord I'd leave the renovations untouched and hand over the furniture and appliances too. He thanked me with a face full of delight, and I thought my goodwill would earn me a decent goodbye. I never expected that the moment we got to the security deposit, his expression flipped, and he said with a mean look on his face: