Landlord here. I own a condo in Seattle that I rent out. (Side note, I'm selling it because the hassle of owning it isn't worth the meager profit it provides.)

You are absolutely responsible for costs incurred bringing it back to livable standards so that it can be rented out again. This includes cleaning, painting, replacement/repair costs for carpets, curtains, appliances, etc. Your deposit is just a hedge against those costs and you can be liable for the actual amount of damage caused even if it's greater than your deposit. It's also completely legit to hire a professional crew to perform the cleaning/repairs. You should also be aware that damage isn't always obvious to tenants. If you smoked in the apartment, for instance, it might need professional cleaning and repainting even though it looked fine to you. Or if you had a pet he needs to remove all potential allergens with a more intense cleaning than usual.

However he can only charge you for damage that you caused beyond normal wear and tear. The landlord cant use you to bankroll replacing old carpets unless you specifically damaged or stained them.

What does your lease say about your obligations to maintain the property and the treatment of the damage deposit? What I've detailed above is more or less standard, but your specific lease may make additional obligations on either party.

Bottom line: The claims as he's stated are probably legit as long as his characterization of the damage is accurate. So disputing the extent of the damage is really the only way you'll get any relief. You both should have taken extensive photos for documentation. Rather than debating the semantics of 'damage' and 'wear-and-tear' ask to see his photographs of the damage he's charging you for along with invoices documenting the costs to repair it. If he doesn't have documentation, show him your photos and ask him to point out the damage.

My advice: If you disagree with his assessment of the damage you can take him to small-claims court to dispute it. If you didn't take any photos then this is a $500 lesson in documenting your rentals when you move out.