You can bid on one of the 19 million items currently offered on eBay — everything from vintage motorcycles to brand-new computers to gently used designer gowns — and score an amazing deal. Or you can put something of your own up for auction on the gigantic online site. But seller beware: If you think you can simply unload all that useless junk in your attic and make a killing, you’re in for a letdown. A whopping 53 percent of all items posted on eBay receive no bids; another 20 percent get only one!

On the bright side, nearly 750,000 Americans report eBay as their first or second source of income, so there’s good money to be made. Whether you’re selling or buying, before you start clicking, here’s what you should know:

If You're Buying...

Creative Spelling
When looking for a specific item, type in a common misspelling of the product in the search field, advises Marsha Collier, author of Santa Shops on eBay. You may find a hidden gem. For example, if you’re looking for a deal on, say, a raincoat, try Burburry instead of Burberry. Want pricey shoes for a song? Try Cole Hann instead of Cole Haan.

Every Penny Counts
Small change can make a big difference. When you’ve determined your maximum bid, add a few cents to the amount. If another bidder closes out the auction with a final offer of the same dollar amount, you’ll win.

Better Than Cruise Control
Don’t feel like sitting at your computer all day? Consider using eBay’s proxy bidding system, which automatically raises your bid in increments ($1, for example, if the item is between $25 and $100; $2.50 if it’s between $100 and $250), depending on the previous top bid. All you have to do is pick the highest price you’re willing to pay — no one sees it but you — unless someone else tops it.

If You're Selling...

eBay Loves You!
The site wants you to get the best possible price. It tells you how to describe your item and how to photograph it so bidders know exactly what they’re getting. And it offers tips on pricing. Once you’ve made a sale, eBay helps you figure out how much to charge the buyer for shipping. Note that eBay takes a small commission from each of your sales.

Will Others Want Your “Treasure”?
Before listing your item, figure out the demand. Visit other auction sites — such as Amazon Auctions (auctions.amazon.com) and ePier (epier.com) — to make comparisons before setting your price. Also check out eBay’s “Completed Listings” link, which will tell you what similar items have sold for in the previous two weeks.

For a Limited Time Only
Auctions on eBay run from 1 to 10 days. According to Dennis L. Prince, author of 101 Ways to Boost Your Fortune on eBay, an auction that spans two weekends attracts the most customers. So start and end your auction on a Sunday, and be sure to close your auction at a time that accommodates both East and West coasters (between 6 p.m. and 8 p.m. Pacific Time is ideal).

Call In the Reserves
When you post your listing, include a “reserve” price, seen only by you, that sets a minimum amount you’ll take for your item. If that minimum isn’t met, you don’t have to take the highest bid. But if the highest bidder was close to your reserve, e-mail her and let her know. She may be willing to come up a few bucks to meet it or negotiate a price you can both live with.

Ship From Home
Once you’re ready to send your item to a buyer, save time by skipping the trip to the post office. USPS and UPS partner with eBay, so you can print mailing labels — already filled in with the correct addresses — straight from the site. Both companies provide free pickups and USPS also offers free packing supplies.

If You’re Really Lazy…
Or if you’d like to sell on eBay but don’t have time, consider letting someone else list, sell and ship your stuff. There are more than 1,000 locations in the U.S. where you can drop off an item — including some UPS stores — and they’ll take care of the rest. They’ll also take a hefty commission, typically around 30 percent, but that’s better than having an item sit around and not earn you a dime!

Next page: The priciest -- and weirdest -- things ever sold on eBay