How much money you make depends mostly on the work you put into it, and for how long.

If you have a regular seller account that is not a paid account, do not expect to make money fast. With only a few auctions up at a time, it will be hit and miss. If the reason you are selling is only for the occasional expensive card or occasional large lots of cards, this could be very economical.

Paid accounts have the benefit of being able to sell in large quantity and have a storefront. With lots of cards out there, people will be able to find what they are looking for more easily.

Exhorbitant shipping costs also impact sales. Most bidders will add the cost of the card plus shipping to see whether it is in their price range or not. Combined shipping helps, but only if you have enough things up that a regular bidder can fine several things he is interested in.

Here are some real numbers from a some real sellers, so you can see for yourself (each block is a different seller's storefront):

 ---------- ------ -------- --------
| month    | year | number | amount |
 ---------- ------ -------- --------
| January  | 2008 |      2 | 100.92 |
| February | 2008 |      8 | 104.74 |
| March    | 2008 |     15 | 403.89 |
| April    | 2008 |     18 | 305.09 |
| May      | 2008 |      9 | 263.97 |
 ---------- ------ -------- --------

 ---------- ------ -------- --------
| month    | year | number | amount |
---------- ------ -------- --------
| January  | 2008 |      3 | 370.12 |
| February | 2008 |     11 | 162.98 |
| March    | 2008 |     13 | 337.52 |
| April    | 2008 |     25 | 608.30 |
| May      | 2008 |     14 | 386.65 |
 ---------- ------ -------- --------