Solver's wrong about end of puzzle? Count last words (5,9)
I believe the answer is:
yours sincerely
'last words' is the definition.
The definition suggests an adverb which matches the answer.
'solver's wrong about end of puzzle? count' is the wordplay.
I cannot quite see how this works, but
'solver's' could be 'your' (belonging to you the crossword solver) and 'your' is found within the answer.
'wrong' could be 'sin' (wrong can mean a sin or crime) and 'sin' is located in the answer.
'about' could be 're' ('re' means regarding or about) and 're' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for yours sincerely that I've seen before include "so long" , "way of ending letter!" .)