Need Advice - Selling Cards Online

So I've been toying with the idea of starting to sell some of my extras on eBay as a way to partially fund my ongoing card purchases (Don't worry, I'll still keep plenty of stuff around for trades.  :)  ).  I know many of you sell some cards online, so I thought I would solicit my fellow bloggers for advice.  Tips on any topic would be welcome - Should I limit how many listings I have active at once? Do you find selling lots of common cards worthwhile? Shipping - how much to charge? Ship internationally or just US? Any issues with managing Paypal payments?  Any problems you've had I should watch out for? etc, etc, etc.....

Perhaps most importantly, do you find the money you make justifies the effort??

Thanks in advance!

Buy It Now~!

This made me laugh.  This card is currently listed on eBay:


Undeniably an awesome card, and one I would love to own personally.  But check out the "buy it now" price:

http://www.ebay.com/itm/2010-G-Monsters-Mesozoic-Ankylosaurus-RARE-/220766315776?pt=US_Baseball&hash=item3366b2a500

Come on dude, let's try to stay somewhere in the vicinity of reality here.  But hey, at least he is offering free shipping...