@maglib "Non-ad-valorem assessments are based on the improvement or service cost allocated to a property and are levied on a benefit unit basis, rather than on value. they are NOT considered property taxes for Schedule A."
This is incorrect, which is why I was waiting for input from the customer.
Real property taxes can be deductible, even if not ad valorem, if they provide a general community benefit and not a property-specific or "local" benefit. For example, a $50 charge per house for community ambulance service is a deductible property tax, while $50 for streetlights (that is only charged on streets with street lights) is a property-specific benefit and is not deductible. (However, taxes charged to maintain or repair existing local benefits are also an allowable deduction.)
This has been a matter of dispute between the IRS and California over "Mello-Roos" taxes, which are a way for communities to raise money without breaking the state property tax cap. The California FTB was denying deductions for Mello-Roos taxes but the IRS has stated in a letter that they can be deductible if they pay for a general community benefit. Eventually the FTB agreed to accept the IRS position and stop challenging the deduction.
Personal property taxes must be ad valorem, but the same limit does not exist for real property taxes. Rather, "Assessments on real property owners, based other than on the assessed value of the property, may be deductible if they are levied for the general public welfare by a proper taxing authority at a like rate on owners of all properties in the taxing authority’s jurisdiction, and if the assessments are not for local benefits (unless for maintenance or interest charges)."
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