For starters, activity on eBay surges immediately after the holiday season. "The first month of the year is a very active month on the selling side, particularly for fashion," said Vincent Payen, eBay's head of consumer selling.
For those looking to auction off their apparel, Payen recommends kicking off on a Sunday between 6 p.m. and 11 p.m. ET and running for a full week to maximize bids and higher sales prices.
There are also a slew of more specific sites for selling everything from electronics to earrings.
Reverb.com is another peer-to-peer marketplace like eBay but specifically for buying and selling music gear, like DJ equipment, guitars, keyboards and accessories. Electronic gear, and particularly effects pedals, which range from $50 to $200, sell best, according to Reverb's founder and CEO, David Kalt. (Sellers pay a fee of 3.5 percent of the price the item sold, compared with eBay's 10 percent.)
Sites like Cardpool, Gift Card Granny and Raise are great for unloading unwanted gift cards. Sellers can earn 80 cents or more on the dollar, depending on the popularity of the brands (more for Apple, less for Old Navy). Some work like exchanges, while others are marketplaces, which may take longer, but could help you get a better price.
Gazelle.com lets you trade in electronics like phones, iPads or laptops for cash. You can currently sell a 128 GB iPhone 6 for about $180, according to the company.
When it comes to designer duds, The RealReal, thredUP.com or the Poshmark app will all process, price and sell your clothing for you. On The RealReal, you can also consign jewelry, handbags and high-end home goods and they'll even send someone to your house to pick up your unwanted items (and take a 30 to 40 percent cut when they later sell).
But regardless of the venue, there are ways to make sure that your product is primed for sale, the experts say.
In any context, a good picture is worth a thousand words. That means it should be well-lit (Reverb's Kalt said natural sunlight is best) and include plenty of additional photos at other angles and close up (eBay's Payen suggests at least six altogether).
But don't skimp on the title and description either — including the manufacturer, item type, size, material and color, to help bidders find you in a search. The more information you provide, the more searchable your item will be, Payen said.
Finally, details like whether there are nicks or if it comes in the original packaging, in addition to where it was purchased and how many times it was used will also boost your credibility, Kalt said. "Be honest about it," he said, "people love that."
(And if you just don't want to bother, consider donating it to charity, Glaser said. You'll get a tax deduction come April, as long as you keep a receipt of the donation.)
Correction: Cardpool is a site for unloading unwanted gift cards. An earlier version misstated the name.