Face to face trading is really risky especially when you are transacting huge amounts of bitcoin. Chances of being robbed by someone is high since people are different. Bad intentions do really happen since we are talking about money. In my case i do only buy bitcoin through online and its better and quiet safer as long you buy on the reputable sites.
The amount is an important factor to consider, thank you for pointing this out! AFAIK there were cases when dealing in real life someone robbed his partner. I think, there's an amount where it doesn't worth for anyone to risk a real life robbery at a public place, but after a certain limit you cannot imagine how dangerous people can be and in real life, you're there with your real life. That's an important thing that you're risking.