Merchant banks to try out an account provider (11)
I believe the answer is:
storyteller
'an account provider' is the definition.
(a storyteller provides an account of something)
'merchant banks to try out' is the wordplay.
'merchant' becomes 'seller' (seller is a kind of merchant).
'banks' indicates putting letters inside (bank can mean to surround or border).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'to'+'try'='totry'
'totry' is an anagram of 'toryt'.
'seller' going around 'toryt' is 'STORYTELLER'.
(Other definitions for storyteller that I've seen before include "he retails pork pies" , "Raconteur" , "Relater of tales; liar" , "novelist?" , "Dishonest retailer" .)