OK, it’s hardly whitecollar crime, especially when you consider that a lot of these dodgy deals are done with and by tradies.
If you have a genuine concern, identify the payments for work that you think were illicit and send a letter to the strata committee and strata manager asking them to verify that these were legitimate payments.
If you get no reply withing two months, a rejection, or an unsatisfactory response, commence proceedings for mediation at Fair Trading with a view to taking the matter to NCAT. Fair Trading mediation is free but it is a prerequisite for Tribunal action.
If there have been dodgy deals, then those responsible may just refund the amounts rather than have their reputations trashed by exposure at Fair Trading and NCAT hearings.