My wife and I had a similar interaction several years ago. A Detective showed up at our apartment door, proper I.D and all, very pleasant, and told us an anonymous tip had been received that we were making and selling Meth from our residence. They had even run surveillance on our residence for several days....seeing us in and out with our granddaughter, me with my guns going to the range, etc., etc.
We invited him in, and had a pleasant conversation. My wife even suggested he take a look at our son's bedroom. He didn't. He then asked me if I thought any of my co workers might have done it. I said I didn't think so, not wanting to get anyone in trouble. Next day, a co-worker who had a reputation for planning, then admitting complex, but immature malicious to vicious "practical jokes" chuckled when he asked about the incident, and he knew much more about it than I told. You "know", but can't prove. :banghead: He said, "I didn't make that call." He probably didn't, possibly talked a friend or relative into doing it for him, so he could say that "honestly", under oath.
Anyway, my wife , who was highly-skilled paralegal, talked to her boss about it the next day, and was told: "NO", wrong response!
He said; Do not EVER let a LEO into your residence without a warrant. Be polite, answer questions or not, don't lie, but once inside your home, if the Officer sees something unrelated to his visit, but still illegal, he can make an arrest. Don't give anything except basic information, and don't hesitate to ask for an attorney.
Now, as for the naivete of the OP,(He seems like a very nice guy!) in this day and age, advertising GUNS FOR SALE in a public forum (radio, sign, classified ad) may not be the wisest of actions. There seems to be some sort of honor code among the majority of gun owners, which has been remarked on several times over the years, which doesn't seem to extend to the general public. No disparagement of forum (this and others) members.
His verbal diarrhea speaks for itself. But, some people are like that...can't shut up to save themselves.
So, maybe he sold a gun,(good for him) and made a friend of the Officer, (a Good thing) but...maybe not.
He obviously has not thought of possible consequences of his actions. In my interactions with larcenously-inclined human beings, that was always a red flag. "He/She is telling me TOO much
...what are they hiding?"
Soooo....do what you want, but remember the timeless counsel "Be harmless as doves, yet wise as serpents!"