Scammers (and legitimate people) use Western Union because it doesn't have Paypal's feature of "if you're not happy, we'll refund the money." So, you get a bad money order. You deposit it and think you have money. You use Western Union to send off the left-overs to the scammer and ship your book. A few days later, the bank discovers you deposited a fraudulent money order and removes the deposited amount from your account. You can't "repeal" the Western Union transaction and you can't call back your package. Scammer has book and money, and you have squat.

Wester Union is used as a scam by SELLERS. You, as the victim buyer, wires them money....and they send you squat. Now you have to go to the police.

- Jim