Only items of quality, every one for my pleasure (3,2,3)
I believe the answer is:
not at all
'one for my pleasure' is the definition.
(both can mean 'you're welcome')
'only items of quality every' is the wordplay.
I cannot quite see how this works, but
'items' could be 'tat' (I have seen 'Shoddy items' mean 'tat' so perhaps 'items' could also mean 'tat') and 'tat' is found within the answer.
'of' could be 'o' and 'o' is located in the answer.
'every' could be 'all' (similar in meaning) and 'all' is present in the answer.
A single letter 'n' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
(Other definitions for not at all that I've seen before include "By no means - polite disclaimer" , "Don't mention it!" , "forget it" , "Anything but!" , "In no way" .)