Earlier quoted context omitted.
> The copies are extremely good, and I suspect not many people in the US are going to spend the time to check if a $10 or $20 is fake. Many places will at least use the marker test on a $20.
From the article, the seller claims that the bills will pass the pen test, so that wouldn't help.
Hopefully it's obvious that the seller mentioned in the article is probably not making or selling a darn thing. What authority are you going to go to when you find out the counterfeit currency you bought online anonymously with bitcoins was just a scam? His scam is, on a small scale, more profitable than actually manufacturing counterfeit bills and selling them.
Which doesn't mean the seller won't get a visit from the US secret service if he's crazy enough to be running this scam outside of Russia or Nigeria or something...