Apex domains cannot have CNAME records.
Question and response
Question
dig address-for-sale.com. NS
Answer
address-for-sale.com. 4 NS ns-670.awsdns-19.net.
address-for-sale.com. 4 NS ns-1249.awsdns-28.org.
address-for-sale.com. 4 NS ns-845.awsdns-41.net.
address-for-sale.com. 4 NS ns-1411.awsdns-48.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0