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Published: Sep 10, 2015 8 min read
eBay on laptop
Ian Dagnall—Alamy

To celebrate its 20th birthday, eBay is offering big discounts during a "20 Days of Deals" event and is hosting a special two-day "summit" that starts Thursday at the San Jose Convention Center.

The convention is focused on businesses and serious independent sellers who aspire to make good money—perhaps even a good living—from moving merchandise on eBay. We thought the arrival of eBay's big anniversary would also be a good time to reflect on the many times when it seemed easy even for novices to cash in by flipping suddenly hot items online for quick profits.

We're talking about crazes like the one that occurred this past spring, when the release of Lilly Pulitzer designs at Target crashed the retailer's site—and when anyone who managed to get their hands on the quickly sold-out merchandise could sell it for a handsome premium online. From McDonald's Big Mac "secret sauce" to a long list of must-have sold-out toys that appear like clockwork, frenzies over suddenly hot goods pop up quite regularly. With each comes the opportunity to make some money by buying low and selling high.

After consulting some experts and gathering research, we've assembled a list of tips to keep in mind if you're trying to play this game. The strategies aren't limited to eBay, mind you. In most cases, they're just as valid if you're selling on Amazon, Craigslist, or any other outlets.

Keep up with the trends. Sometimes a hot, must-have item pops up totally out of the blue. For instance, few people predicted that a robotic hamster (a.k.a. Zhu Zhu Pets) would be the hottest toy of the 2009 holiday season, selling for an enormous premium online to parents desperate to please their kids on Christmas morning.

More often, however, someone who is paying attention to pop culture and shopping trends can make an educated guess as to the kinds of items that will be in high demand among rabid fans. Target has a long history of partnering with trendy designers like Missoni and Lilly Pulitzer, and the results have typically been near-instantaneous sellouts followed by higher-priced resales at eBay. Likewise, you didn't need the Force to foresee that, among other Stars Wars merchandise, the remote-controlled BB-8 Droid from the forthcoming "Star Wars: The Force Awakens" would be an instant hit—and will probably be in high demand for months to come.

Danna Crawford, a.k.a. the Power Selling Mom, who has been a seller on eBay since 1997 and is attending eBay's 20th anniversary convention this week, advises would-be sellers to take a close look at Sunday newspaper circulars and advertisements to see what products are being pumped up. "All the big box companies have done their homework," she says, and they'll be promoting the items that are most likely to be popular among shoppers.

Plan ahead. Even if you think it's crazy to wait in line for hours to buy the latest iPhone or retro Air Jordans, the fact that people will endure such situations should be a sign that these items will be hot sellers online. When you have a good idea that a soon-to-be-released product will be in high demand, figure out all the particulars, including when the item will first go on sale online, and/or what stores in your area will have ample supplies.

It's obviously easier to do your shopping in your pajamas on the couch, but there is a risk of getting shut out: Target's website crashed this past spring when the Lilly Pulitzer collaboration was launched. Then again, waiting in line for a store to open is a time suck, and the in-store shopping experience can be frenzied at first.

React quickly. Even if you don't know of a hot item in advance, there could still be time to react and profit from a craze. But don't sit on your hands. Hop into action as quickly as you can. If a retailer's website is sold out, check out the possibilities of a "buy online, pick up in store" option near your location. Shop frequently, because whenever possible stores are replenishing their supplies. Play your cards right and you could profit handsomely. One man reportedly made $6,000 in a couple months after quickly jumping on the Zhu Zhu Pets craze a few years ago.

Think: limited supply, limited time. If anyone could buy a $100 unlimited Olive Garden pasta pass anytime they wanted, there would be no reason someone would be willing to pay extra. Same thing goes for the "exclusive" $450 Starbucks gift card that went on sale for a brief time a couple years back. But because these and other items are sold in limited supply, for a limited time, people who are left out have a tendency to, well, feel left out—and are often willing to pay well above the retail price in order to play along and get bragging rights.

Strike while the iron is hot. "The biggest lesson I've learned about selling on eBay is to sell, sell, sell when the market is hot hot hot," says Crawford. "Do not sit on items too long, thinking more money can be made later because when the market peaks, it will soon wind down."

Be smart about listings, prices, and service. Among the most common eBay selling mistakes are typos or vague descriptions in listings, poor (or no) photographs, the failure to answer questions, and charging too much for shipping. Get the basics right or you'll be shooting yourself in the foot in terms of closing sales. Also, curiously, research has shown that sellers who use quirky, "precise" "Buy It Now" prices like $137 or $84 tend to yield higher sales prices than those who use big round numbers in increments of $50 or $100.

Don't get greedy. "I've seen it over and over again with eBay sellers making this huge mistake," Crawford says of eBay sellers trying to wait for already high prices of Tickle Me Elmos, Beanie Babies or whatever the hot item of the moment, to go even higher. But this is an extremely risky game to play. "I feel, take the money and run because when greed sets in, empty Paypal accounts are not far behind."

Note return policies. Before maxing out your credit card and filling your garage with Star Wars merchandise, Nike Air Max LeBron sneakers, or some fancy new gadget you are convinced will be in extremely high demand, take a close look at the return policy where you're making the purchase. If the craze you foresee doesn't crystallize to the extent you were hoping, you could be literally stuck holding the bag—lots of bags, in fact. On the other hand, if sales turn out to be a dud and the store's return policy allows you to bring the unsold items back, there's no harm done.