I mean, let's put aside whether the person might have reasoned the other party was willing. This line of reasoning is ridiculous. If someone appears 100% willing to you, and there's absolutely nothing different from a genuinely willing person, why should you be at fault because somebody else put that person under duress, or because they were lying (under duress or otherwise).
If someone does a 100% legal thing according the information they know, and is not otherwise negligent, there is no crime they should be charged with. As it happens, in the US, statutory rape is the only one I'm aware of that does not follow this criterion; even manslaughter requires negligence (although I'm not making a point about that).
> somebody else put that person under duress, or because they were lying (under duress or otherwise)
It's like benefitting from any other kind of traffic, isn't it? If you benefit from a money laundering scheme or a fraud, you'd be charged with complicity, even if you took a lot of care into not inquiring about the provenance of the money. At least, that's how it's be judged in my country (France, and I'm not a lawyer so don't quote me on that). I can't tell for other countries.
If someone does a 100% legal thing according the information they know, and is not otherwise negligent, there is no crime they should be charged with. As it happens, in the US, statutory rape is the only one I'm aware of that does not follow this criterion; even manslaughter requires negligence (although I'm not making a point about that).