An average and a below average buy at the greengrocer's (7)
I believe the answer is:
parsnip
'the greengrocer's' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'an average and a below average buy' is the wordplay.
'an average' becomes 'par' (average score in golf).
'and' is a charade indicator (letters next to each other).
'a below average buy' becomes 'snip' (I am not sure about this - if you are sure you should believe this answer much more).
'par'+'snip'='PARSNIP'
'at' acts as a link.
Can you help me to learn more?
(Other definitions for parsnip that I've seen before include "A white root vegetable" , "Type of root veg" , "Pale carrot-like vegetable" , "Tapering vegetable" , "Sweet root vegetable" .)