Regardless of almost anything you're trading, it should take place in a crowded place during daylight to minimize risk.
We are normally cautious when we are trading for the first time with someone. But if we are dealing with some person, who has been doing trade for a long time with us, then sometimes we ignore the negative consequences, and get somewhat relaxed. Normal people tend to trust strangers after a few nice deals. And conmen are quick to exploit this trust.