"We did a whole host of due diligence but when you're lied to, it's hard to find," Are you kidding me? That's the whole purpose of doing due diligence in the first place.
I have a hard time grasping this. If the books are in order, I wouldn't expect to later find significant fraud affecting the books. For example, if the books show $x in orders pending, I'd sample the orders to verify within some confidence level that the lot is worth $x.
And one of the mistakes you should be looking for is the possibility that you are being lied to so thoroughly that it's hard to know what's real and what isn't. It's in situations like that, that forensic accountants earn their salt.