Q:

Listening in in a negotiations

Consider the following situation:
A businessman B is negotiating with a group of foreigners C who are widely (and with a reason) suspected of having an "alternative" view on business ethics. B thinks that the crooks might betray themselves by talking to each other in their language which B does not understand, so he asks his friend F (who is a native speaker of the foreign language) to listen in on the negotiations (from the next room when negotiating in person or on a second phone line when negotiating over the phone). So, C do not know that there is a third party F listening to the negotiations. 
Alternatively, B records the conversation (without C's knowledge) and lets F listen to it off-line.
If this behavior unethical?
Obviously, the answer may depend on the country in question (I have the story from F who was quite proud of his role), so let us limit ourselves to USA (and the West in general).
Follow-up.

A:

I'm not sure why you're negotiating with people you think aren't ethical.
I'm assuming the result of this negotiation will be a contract. What value will that contract have? It's very expensive to go to court and force someone to do something against their will.
Even worse if the foreigners discuss their intention to do something and then later do it, you have to acknowledge in court that you were warned in advance.
It seems to me that you're voluntarily walking into pain for yourself.

