safest way is you bring a gun tucked behind your back. remember to fold over your shirt, you don't want it sticking out.
maybe think about a hunting knife too. that can come in handy for hand to hand combat.
No this is why you should meet in a public place. Nice thing is with phones now a lot can be a hotspot and you have instant wifi. Can meet at McDonalds, or a police parking lot, I mean tons of places.
One big thing with a face to face only bring what you need. Do not bring your cold storage, or more then buyer is buying.
If you suspect you need a side arm you should not be going. There is too much risk or something is not right.