Most states require you to show firearms purchaser IDs, called FID in my home state as well as a drivers license.
To acquire a FID, you need to go through a background check. This is how you are meant to know if the person is "safe to sell to".
If people in state X have a problem with that, then they should get together and find a solution to it.
Until then I don't think I can justify to myself censoring an otherwise completely legal discussion, especially when such a discussion can be used as a record of a sale that would otherwise not be present.
That's just my two cents.
Minor point, but there aren't that many states that have firearm purchaser IDs. NY, NJ, MA, IL are a few, but most states don't require anything more than a driver's license.
A: "I have this gun I"ll sell for $400." B: "I will buy it from you." A: "Ok. Let's meet at the police station parking lot. What time is good for you?" B: "How about 5:30?" A: "Ok, see you there."