bro ultimately its just ure word against his
more credit to him rather than u

y
cause u did not check the mobo before u sold it...
u knew it was a replacement mobo and u should have checked it.

try to put ureself in that position. u cant use the guarantees of another to pass it on to the person u sold to. the guarantee has to come from u.
in this case if in ure initial thread u did not put any form of guarantee on ure part then u have a case of ethics only here.

in writing.. ure right