> I think that example breaks down for the laymen understanding of a transaction, since the robber is a different party than who gave the coins in the first place.

The government is certainly a different party that wasn't involved in the original transaction, right?

> What if an employer paid you in coins, so you take your coins and go home, then tomorrow your employer decides to take back the coins they gave you since they were not happy with your work (or they're just jerks)?

This can definitely happen, at least with checking accounts. It has happened to me once because an employer accidentally double-paid everyone, and they were able to withdraw one of the payments from our accounts. I'm not sure exactly how that works. It could just be that your employer essentially has full access to your checking account since you gave them your account and routing number. Incidentally, I was always curious what would have happened if I had moved everything out of my checking account before they make the correction. But regardless of how it is actually implemented in the banking system, it's pretty clear if your employer erroneously removed funds from your bank account, or if you cashed out the accidental second payment then quit your job, it would again just come down to the legal system.