If some guy claiming to be a Russian general offers to sell you what looks like a surplus nuclear warhead, how do you know he isn't a CIA or FSB agent running a

If some guy claiming to be a Russian general offers to sell you what looks like a surplus nuclear warhead, how do you know he isn't a CIA or FSB agent running a sting? How do you know that he hasn't ripped out the electronics that control the timing of the implosion and sold them to someone else? How do you know that the guy who assembled that particular warhead back in 1973 was sober and followed all the instructions? (If you have eighty nuclear warheads in your arsenal, you have a credible nuclear deterrent even if each warhead has a 75% chance of being a dud. If you have one, not so much.)