Happens with HMRC, too.
People seem to assume that what happened in the past will never come to light, which is all well and good until answers are demanded to difficult questions. In the case of people flipping stuff on ebay, it takes one request to gather a complete record of historical transactions and soon all payments will also be handled by ebay, which will leave no room for any benefit of doubt.
Electronic accounting makes such investigation rather simple and it's entirely possible that the Exchequor might soon find themselves looking at all manner of revenue losses, given recent government borrowing.