If you sell here, the Police will ask for/subpoena the records of PMs and Posts for the transaction. We will oblige and provide your proof of innocence.

If you sell on gunbroker, you have proof via their records.

If you sell via Email, save the emails.

Having another person there will add a good witness if it ever comes to that.

It is a good Idea to keep a piece of paper, with the serial number, model and the sale date, even if it isn't a BoS signed by other party. Then you can tell police "Yep, I sold that one on date XX-XX-XXXX."

They may come knocking on the door, and even if you don't have records or witnesses of any sort, they need a lot more proof that you did the crime than the fact that you once owned the gun. Our wonderful legal system requires them to prove you DIDN'T sell the gun, not the other way around.

To the original question:

Many of us like selling here, because of the feedback system. You can check out the feedback left for any potential purchasers, and their post history. You can even say "No buyers without feedback on the site" in the ad if you wish.
Depending on how many people I have met and trust before have vouched for the buyer, I may or may not bring along a friend to "help"
I always CCW at any transaction, even people I've dealt with before and trust.

Scams: If someone wants you to send a firearm to them, send it to an FFL. One that you pick out of the listings in their area, not that they provide. Watch out for the standard fake money orders, etc. Work only in cash if you haven't dealt with the person before, no matter what the circumstances.

I have met at sporting goods stores or shooting range parking lots most of the time. People less likely to freak out if they see a gun around there. Plus to the shooting range for the buyer, if anything looks fishy/questionable in quality you can go in, pay your range fees, and test it out before committing.

Hope these help.