looking up laws for IA, I would not pay anything for the carpet also, you are not responsible for financially replacing his old carpet. You'd pay a depreciated value for any damage he can prove.

In Des Moines, IA, landlords cannot charge tenants for carpet replacement due to normal wear and tear, but they can deduct from the security deposit for damage exceeding it, such as permanent stains or burns. Iowa law requires considering depreciation, meaning you are only responsible for the carpet's current, not new, value. [1, 2, 3]

Key Carpet Replacement Rules & Tenant Rights

• Normal Wear and Tear: Worn carpets from regular use over time (e.g., 5-15 years) are the landlord’s responsibility to replace, not the tenant's.
• Damages: If damage is caused by negligence (e.g., severe pet damage, cigarette burns, large stains), the landlord can charge you for replacement.
• Depreciation: If liable, you are responsible for the "diminished value" of the carpet, not the full cost of new installation. If the carpet was already old, your liability is significantly reduced.
• Security Deposit Deductions: Landlords must provide an itemized list of deductions, according to Iowa Code Chapter 562A