yur bank account is no different from a post office account - you could quite easily get your income, then take it out at the cashpoint or at the bank in cash, just as people with po accounts do. therefore they are NOT looking to see WHAT you spend your money on and making judgements which you seem to be implying (how could they? if you had a 50 pound debit card transaction for sainsburys its not like they can tell whether you bought clothes, fruit, chairs, or booze and fags) On the cntrary, they are checking to make sure you are not having any extra undeclared income going IN to your account for example money you are getting cash in hand for work you are doing.
They will not know you bought a bra, no will they care. The only thing i can suggest is that if you want the benefit, comply with the conditions, if you dont want to comply then dont apply for the benefit. If someone had a PO account, they would be checking for the same thing