- http://shadowlife.cc/2012/11/secure-and-professional-bitcoin-otc-exchanges

I haven't completed all that many in-person trades myself but more than once now I have been asked to sell for cash an amount of bitcoins larger than any amount I would be selling by myself.  But had I previously gotten in contact with other traders in my area a larger trade amount probably could have been arranged since that would allow me to have to trade only up to my personal max level and then also there would be two or more of us present when the cash traded hands.

As far as buying bitcoins from an untrusted stranger, the risk of double spending (due to either a Race attack or a Finney attack) is significant enough to require at least one confirmation (or a Green address transfer or a service such as a LocalBitcoins "Transaction" where the funds released to the buyer would always be already-confirmed funds).

One challenge with in-person trading is with communications and coordinating the meet.  Unless you are already planning on spending a couple hours at a coffee shop or wherever, make sure to specify in advance your expectations otherwise you'll often be stuck waiting for your trading partner to show, oftentimes in vain.

For a recent trade the buyer arrived on time but he needed to get cash from an ATM.  It was only then that he learned that his bank account has a low maximum daily withdrawal amount, leaving me holding more bitcoins (and less cash) than I had planned.  Had I confirmed that the buyer had cash in-hand before even setting a meeting time and location is something that would have saved me time, money and the resulting headache