When doing a sale, I put rifles or handguns in a poly gun case in the trunk so they can be easily viewed and handled. If I am buying or selling I will tell the person I am going to meet if I am bringing someone with me and I expect the same info in return. If a guy shows up with a couple of guys he forgot to mention he was bringing its a no deal. I'm outta there. I have had one incident like that and don't need anymore.
I have done 5 FTF's the past two months and all went well. I have met some great guys, all members of ARFcom. That incident I mentioned above? Well I went from my usual orange alert, begins the moment I step out my front door, to full red alert in the parking lot that day.
Meeting at Lowes, Wally World, Home Depot and some other places mentioned in this thread are all good and as Wilson generally said, don't go waving your weapon around like it was a flag and draw the wrong kind of attention.