I went through one of those with an item I placed on Kijiji.
What is going to happen is that you most likely will get a Bona-Fide looking MO drawn on one of your local banks and it might be sent by overnight Fedex!
It will be for an amount possibly $1000.00 higher than your item is worth, you will be asked to cash the MO, take out your $100.00 for e.g. and send the rest to someone in, who knows where, an address will be supplied for you to Wire him the money, but you MUST do it right away.
3 weeks later you bank will advise you that the MO is bogus and you are on the hook for the whole amount.
I took the MO to the bank and got them to verify its validity and they told me to tear it up.
But he said it would most likely have got past a teller, especially if you had an account at that bank.