A further word of advice -- even dealing in cash. buy one of those 'pens' that highlight money, and 'test' the cash like merchants do now mostly with bills larger than $20. It can tell you if that specific bill is fake or real. Even the Feds admit, counterfeit money is so real-looking and feeling, it's difficult for the professionals to tell if from real bucks anymore.
I know, I know, we're all getting so paranoid every deal we do seems like a criminal act ... but it pays to be as safe as possible when dealing with large transactions.