Ask the people convicted of soliciting a prostitute?
Not a lawyer but had a brief introduction to the entrapment defense as a youngster. As explained to me, in the US, an entrapment defense requires the prevention of choice on the part of the criminal.
So if the LEO offers the converters and the guy says "Get out of here with those things!" then no arrest and no entrapment.
If the LEO says, "I work at a place that replaces catalytic converters and we need to convert these older non-working ones to cash." Then the person making the choice can reasonably say he believed that it was a legal transaction, so even if he is arrested the defense would be entrapment.
I will leave the other script (LEO is the buyer) as an exercise for the reader :-)