Courtney Mirenzi, 29, of Austin, Texas, has always loved thrifting, scouring thrift shops for stylish bargains such as a sequined cocktail dress or designer handbag. Those thrift store finds don’t always come in her size, however, so about two years ago, she started reselling items on eBay.

Now, it’s her main income stream, and her boyfriend helps run her eBay store. Mirenzi also sources pieces from a friend’s closet and splits the proceeds between them.

“My mom always said you should open up a store one day,” Mirenzi says. “I tell her ‘I have opened a store. It’s on the Internet, and the inventory is in my closet.'”

Thanks to sites such as eBay, Etsy (a haven for vintage clothing) and Poshmark (a fashion buying and selling app founded in 2011 that now has millions of users), other creative, fashion-conscious women are doing the same, scouring sample sales, estate sales, thrift stores and other sources for items with resale potential. Some resellers also buy items from limited edition designer collections at Target or other retailers, although Target has cracked down on this practice recently in light of demand for its Lilly Pulitzer collection.

Bethany Nixon, 37, a mother of two who lives outside of Detroit, used to work as a buyer for clothing stores in Michigan and started selling her own finds on eBay in 1999. She now sells items (mainly vintage T-shirts and some handmade goods) through her website RewareVintage.com, which she launched in 2005. She also sells items through Etsy, Instagram and Whurl (an online vintage marketplace where users can post what they’re looking for). Fashion resale has been her main source of income since 2009, and she keeps two rolling racks and bookcases in her finished basement to store inventory.

While many resellers gravitate toward gently used clothing, Amber Ivison, 21, of San Diego, buys handbags wholesale in Los Angeles’ fashion district and resells the bags through Poshmark. Since joining the site in 2013, she’s earned $34,000, part of which funded what she describes as her “dream wedding” in February. “My husband’s in the military, so we’re constantly moving,” she says. “Poshmark has been so amazing because I get to be my own boss, and I get to spend time with him [when he’s home].”

Read on for their tips on finding resale-worthy goods, setting prices and more.

— Know your niche. Choosing a focus rather than selling a little of everything helps you develop deeper product knowledge. Ivison started selling clothing and accessories, but when she realized she was selling mostly handbags (and that bags are easy to buy online because there’s no sizing concerns), she made that her niche. “Pick whatever you’re passionate about because you’re automatically going to be more knowledgeable and have an easier time learning about it or describing it to somebody else,” Nixon recommends.

— Seek quality. You can get a feel for what brands are in demand by checking what brands resale sites like thredUP accept. However, quality and condition should trump brand name. “Brand is important, but if I catch something and it feels expensive, I’ll buy it,” Mirenzi says. “When someone gets something in the mail, they don’t want to get something low quality.” She’ll convey the item’s quality by writing descriptions like “sturdy leather” or “silky soft cotton.”

— Buy low and price to profit. Finding inexpensive, high-quality items you can sell for a profit takes patience and practice. “You need to spend a lot of time digging through racks of clothing,” says Nixon, who tries to buy products for 25 percent or less of what she can sell it for. In some cases, she’ll buy concert tour T-shirts that can bring in $100 or more. “Nirvana T-shirts are highly collectible and sought after,” she says. “Harley-Davidson shirts are really hot right now.” Mirenzi’s local Goodwill outlet in Austin sells clothing by the pound, which helps keep her acquisition costs around $2 or less per item.

— Take good photos. Savvy resellers don’t just snap a few quick smartphone photos and post them online. Since online customers don’t get to see or touch items in person, high-quality photos from multiple angles help seal the deal. Ivison stuffs her handbags so women can see what they’ll look like full and uses seasonal backgrounds when photographing. Then she’ll edit the photos before uploading. “The visual aspect is just as important to me as the actual item,” she says. Nixon also has two mannequins she uses for photographing clothes.

— Disclose defects. If an item has a small defect, Mirenzi will explain it in the description and include a photo so the buyer knows what to expect and doesn’t file a complaint later. “Be honest about your descriptions,” she says. “You don’t want to lie if there’s a flaw in one of your items.”

— Treat it like a business. Lots of people use resale sites sporadically to clean out their closets. That’s a good way to start, but if you hope to make serious cash, you need to provide excellent customer service just as a business would. “Whether you’re selling on Poshmark, eBay or Etsy, make sure you’re going into it professionally,” Mirenzi says. She tracks what she pays for each item and what it sells for, and also promises to ship items within one business day.

That said, expect to learn as you go, and tweak your strategy once you see what works and what doesn’t. “I didn’t go to college,” Ivison says, “but I taught myself to run a business. This is my business school.”

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Inside the World of Fashion Resellers originally appeared on usnews.com