AFAIK, the allegation is that he agreed to sell coins at higher than market value to an undercover agent who claimed to use it for illegal purpose.
As far as you know, or as far as you think you might have kinda maybe seen someone make a thinly veiled unsupported allegation of, though you cannot remember who, what, nor where?
A few people got burnt, now the rest of us should know. "Don't ask, don't tell". If you are the seller, up front say, "don't tell me what you are using these for and there won't be any problems". It isn't that hard. And if somebody then does tell you, well...... good chance they are a cop.