Want to get in the game? Here are some of their top tips for selling whatever you've gotten tired of.
Embrace variety.
"The market is saturated with Coach and Michael Kors, so I like that my inventory is always varied," Tiffany said. "I have some of everything." Don't think that just because a brand is smaller it won't sell. It's the Web: People are hunting for specifics.
Take care of your stuff.
All the sellers we spoke with confirmed that better condition brings in higher prices, so taking care of pieces, from when you buy them to how you store them until they're listed, is vital.
Pay attention to the photos you take.
The better the pictures you post, the more interest you'll create with shoppers. "Take clear pictures of the front, back, sides, interior, exterior, and any hardware, logos, and serial numbers," Caroline explained. "I also include pictures of any wear and damage as well." Skip messy backgrounds when snapping photos, opting for clear, simple surfaces.
Be available to shoppers.
For success on resale apps, think of yourself as a business who wants to make customers happy. Many of the top sellers we spoke to said it's important to answer questions, ship quickly, and to make listings informative. Consider doing free shipping and allowing people to make offers.
Be realistic about pricing.
"Do your fair research on resale value before listing," Stephanie said. "If that pair of jeans is selling for $25 on other websites and you list at $100 simply because you purchased them for $200, you're wasting your time." A quick browse will make some things obvious: Designer bags hold their value; pricey denim doesn't.
Be ruthless about letting your stuff go.
Want to make a substantial amount of cash? You've got to be willing to part with your goods. If you're entertaining any thought about putting it up for sale, do it. "If you're not using it, why not see if someone else might want it?" Tiffany asked. Stephanie operates under the same idea and resists getting attached to things. "I purchased a gorgeous preowned but completely new Louis Vuitton cuff and only used it once in three months. It's a total beauty, but I lost interested and decided to sell," she said. "It's such a large investment to just let sit there without using. I can sell it and buy something else that I'd enjoy more."