Sell genuine ones over end of June (7)
I believe the answer is:
realise
'sell' is the definition.
('sell'->'realize' is in my internal thesaurus and 'ize'->'ise')
'genuine ones over end of june' is the wordplay.
'genuine' becomes 'real' ('real' is associated in meaning with 'genuine').
'ones' becomes 'is' ('I' can be a synonym of 'one').
'over' means one lot of letters go next to another.
'end of' suggests the final letters.
The final letter of 'june' is 'e'.
'real'+'is'+'e'='REALISE'
(Other definitions for realise that I've seen before include "Come to be aware" , "Make concrete" , "Achieve, make" , "Convert assets into cash" , "Tumble" .)