Squander cash on account of what bookie offers? Then stop! (9)
I believe the answer is:
overspend
'squander cash' is the definition.
'on account of what bookie offers? then stop' is the wordplay.
'on account of' becomes 'over'.
'what bookie offers?' becomes 'SP' (short for starting price offered by bookmakers).
'then' says to put letters next to each other.
'stop' becomes 'end' (synonyms).
'over'+'sp'+'end'='OVERSPEND'
(Other definitions for overspend that I've seen before include "Excessive outlay" , "To exceed one's budget" , "splurge" , "Buy too much" , "Use too many resources" .)