There is no official document at least not from anything thats a hard core, irrefutable, bona-fide source of law. (the AGs "enforcement guidance" or whatever its called, doesn't really count, unless we're believing in her fairy tale BS).
If I was in your shoes- I'd tell the buyer to politely f*** off and wait for the next guy, he obviously doesn't understand how the law works vs this AG edict garbage bullshit. he should stick to an O/U or something if he's "afraid".
Usually any buyer that asks me legal questions like that- automatic red flag, automatic do not sell to under any circumstances. Those people are WAY more trouble than they're worth. I almost did it once but after the 4th back and forth it dawned on me that I was completely wasting my time.
-Mike