>>taxpayers don't have ss#, they do have ITIN#<<
Why exactly are you using an ITIN? Your client can not file with an ITIN if he is eligible to get a Social Security number, right?. So using an ITIN must mean he is a non-resident alien. And like the IRS has told you correctly, non-resident aliens are NOT allowed to deduct real estate tax on Schedule A. Check it out in Pub 519.