"If people in the U.S. aren’t suspicious of free money, PayPal payments that look fake, the absence of a payment in their account, fake emails from PayPal’s FBI department or just Nigerians in general, then they deserve to have their money taken from them." I could easily see my parents falling for this. I don't think they deserve to have their money taken. Although, to be fair, I doubt my parents could set up and us…
So I can see how these emails seem totally real and threatening to the average computer-illiterate who sells something for the first time ever. Remember, good scams are about that initial shock, that initial mental blow you deal on your victim to completely catch them off-guard and disable their logical thinking. Flashing a shiny batch or pretending it is an "emergency" is a very good angle.