One interesting point about Western Union. Once someone pays WU, the recipient can pick up the money anywhere in the world. It's not like you send money to a particular WU office. So even in scams that request second or additional payments like this one, there's no way for law enforcement to stake out the particular WU office and catch the scammer. IMO, legislation is desperately needed to curtail the way Western Union does business. Like requiring that money be sent to a particular, pre-determined location (that would be known to the sender), and that photo ID be required to collect.
Also, while there may be a way to track IP addresses, don't expect the seller/scammer to be in the US. And don't expect law enforcement to have any desire to use their considerable resources to help you get your money back. This will NOT meet their "Threshold of Enforcement". The FBI has an Internet Crimes Unit, (ICU) where you can report the scam, and scammer, but don't hold your breath waiting for an arrest. Unfortunatley, the FBI's list of priorities is topped with terrorism, crimes involving nuclear material, murder, kidnapping, slavery, and scams where billions of dollars are involved. No time left these days to chase someone who scammed someone out of $2,800 for a non-existant Bobcat.