People looking to buy them typically use "Ending Soon" to search for cheap auctions ending soon, so you can have your listings end in 1 day (or 3) and gain feedback that way. However, less than half of those people will actually leave you feedback if you are selling and buying/selling too many items in a short time span CAN get you suspended for feedback manipulation.
My personal opinion is that you should go on eBay with about $50 and in the middle of the night, look for single baseball cards at auction (typically from novice sellers) you can buy for .99 cents or less with Free Shipping - they do exist, you have to buy early to mid week late at night. With $50, you can probably buy about 50 or even 60 cards. Simply make sure that they cards have a history of being sold for an average of $1.49+ as a Buy it Now, and make sure the current lowest price a seller is offering the same exact card for is $1.49 or more, so you can undercut him by a penny and make a quick sale. Then when you get the cards, throw up all of your listings to either END as a 7 day auction at Sunday night around 7 PM pacific standard time, or as a Buy it Now but make sure you are the cheapest. You'll earn twice as much feedback this way, as a buyer and a seller, its really easy to do, and you might even make a couple bucks but you shouldn't lose money doing it. I do this with a lot of comic books on new accounts, but my favorite method is with DVD's but if you sell more than 1000 dvds a month it raises some red flags.