Single seamstress, on the surface, is impressed by writer showing candour (8)
I believe the answer is:
openness
'candour' is the definition.
(I've seen this before)
'single seamstress on the surface' is the wordplay.
'single seamstress' becomes 'ness' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'on' means one lot of letters go next to another.
'the surface' becomes 'open' ('open' can be a synonym of 'surface').
'ness' put after 'open' is 'OPENNESS'.
'is impressed by writer showing' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for openness that I've seen before include "Candid nature" , "Frank attitude" , "4 dn quality" , "Candour, receptiveness" .)