Craigslist Scam:
The scam works like this.  They think your item as described is perfect.  They might ask a few questions about it, and then will pay your asking price, sight unseen, because they are never around close by to come look at it (they use the stationed somewhere in the military a whole lot).  They will give you an extra $40 or $50 to old it for them.  Then they tell you they will send a cashier’s check or money order for that amount plus extra for the “shipper”.  They ask you to wire that extra money by untraceable means such as Western Union or Moneygram.  The check or money order turns out to be bogus and you end up out the money you sent plus the bank fees.  Also, if the check is big enough you may end up being charged criminally.  Take the check and the envelope it came in to the post office and have them forward it to the postal inspectors.

In the case of them using PayPal, the same thing happens.  They send a fake email looking like it came from PayPal, get you to pay the shipper, and then find out that the e mail was fake and no money is available.