I am sure it is possible, but not probable to do ebay full time. You would be best suited to have multiple selling outlets, and other ways to supplement your income. Of course, it never hurts to have as low of bills as possible. I've always thought of it like this: Do you really need that nice new shiny car that you pay $500/mo for on a lease ... understanding it is at the expense of staying on the work treadmill for several hours longer each week? I think I'd rather drive around in a tin can, if it frees me up to do what I want.
I am a business owner, so I don't sell cards full time by any means, but I think that helps my case personally. If I did cards full time, it would *feel* like a job. Right now, it is just a super fun hobby that can generate income from time to time. It is funny how, the thought of landing a $1,500 project for my company simply can't touch the excitement of selling $500 worth of cards.
Inventor of the INVISIFRACTOR
I MAKE CUSTOM CARDS
...AND COLLECT CANSECO