If I send the packs to him/her first then they could easily run off and I would lose out on however much it is. I have my reputation from SR and Bitcointalk to lose if I run off with the coins but for the person sending me the coins they can easily make a new account and do the same thing.
It is MUCH easier to get a moneypak or cash load to an ATM card reversed than it is to reverse a bitcoin transaction.