If you receive, at the closing in 2018, a credit or reimbursement for part of the property tax that you deducted on your 2017 tax return, you would not amend your 2017 tax return. The credit or reimbursement is an itemized deduction recovery. You report it as income on your 2018 tax return, to the extent that it reduced your 2017 tax. See the section on "Recoveries" in IRS Publication 525. You can read that section online at the first link below, or download a PDF of Publication 525 from the second link below. The section on Recoveries begins on page 22.
Read online: https://www.irs.gov/publications/p525#en_US_2016_publink1000229391
Download PDF: https://www.irs.gov/pub/irs-pdf/p525.pdf
