Normally when I sell on ebay, I charge a processing fee that is part of my shipping charges. For instance, I'll tell it to calculate shipping based on UPS ground, then add $3 as my handling fee on a modest priced item. This almost sort of covers ebay and paypal's fees.
It is also common for ebay to hold your funds until you either get a delivery confirmation or positive feedback. Considering how many people forget to leave feedback, I'd make sure to use a signature delivery confirmation which of course can add up to $5 to shipping charges and this is NOT calculated by ebay's built in shipping estimator.
I have tried and tried to make the integrated label printing work with ebay. I have created countless ups accounts, given my credit card to both ebay and ups, built an altar and sacrificed an unblemished goat using a dagger purchased on ebay on a full moon. It simply cannot be done.
After having bought a USB memory stick that was supposed to be 4 GB only to find out it was a 256 MB stick "formatted" to look like 4 GB from a crook in Hong Kong, I understand why ebay's policies are so heavily slanted toward sellers. I have never been burned by a buyer but I've had to wait and even add funds to paypal to cover shipping costs because they wouldn't use the proceeds from the pending sale.
As for craigslist, I've never had any luck. I tried buying a used cell phone on CL from a seller offering it for $20 less than the lowest "completed listings" price on ebay. I got in my car, went to the atm and took out the money then called the seller to confirm our meeting. It was supposed to be inside a store but no. This guy wanted to meet me in a dark parking lot and wanted to know what kind of car I drive. I told him I drive a State Police cruiser and hung up. I went back to ebay and bought the phone. About a week later, there was a news story about somebody getting killed when meeting a CL seller to buy a cell phone. It was on the opposite side of town from the guy I was on my way to meet but it was too close for comfort! If you use decide to CL, beware of buyers or sellers that want to meet outdoors in the dark (which comes early in the winter months) instead of a well lit indoor location.