The eBay veteran, who is planning on retiring in August 2024 at age 40, started selling electronics in 2008 after getting laid off. He's been studying the platform for 15 years and become the top seller of men's clothing. According to eBay's 2021 Listing Quality Report, which provides sellers a performance overview of their biggest 10 categories, his eBay store Technsports ranked No. 1 by gross market value in each category.

Richard, who prefers not to share his last name for privacy reasons, knows what works and what doesn't work — and shared two rookie mistakes that could derail your reselling business.

1. Accumulating a 'death pile' by sourcing and not listing
There are two main steps to selling on eBay: sourcing items and then listing them.

The sourcing — shopping at flea markets or thrift stores for items to resell — is typically considered the fun part of the process, "but if you just source and don't list, you could be in a world of problems," said Richard.

He added: "The 'death pile' is where you shop all day, you bring it home, and then you go out and shop again and forget the listing portion. The listing portion is the bulk of the work. It can be tedious, it can be a process, but that's the work."

He recommends setting a schedule to maintain discipline: "I'm going to source at this time, I'm going to list at this time, I'm going to pack at this time. We can't just source all day; otherwise, we will source ourselves out of business."

2. Focusing on items you like, rather than what the customer likes
It sounds obvious, but you want to buy items that will sell. A common mistake is listing items that you think are cool before looking into whether there's demand.

"The market is the market. The market dictates what a good item is and what a bad item is," said Richard. "If you had some item that you think is rare — like a limited-edition pencil eraser — maybe no one is looking for that item. And if we spend all of our time sourcing and listing these items that we think people are looking for but they're not actually looking for, then we have a lot of money tied up in our inventory and not in our bank account."

It's an easy mistake to avoid: Assess the market. Spend time browsing the "sold items" section of your category on eBay to figure out what is selling well and what isn't. Study your category for 30 minutes a day, he advises.

It'll help you avoid an inventory backup. Plus, it'll help you identify extra-profitable items.

For example, Richard, who specializes in pre-owned clothing, figured out that while a regular Nike Dri-FIT shirt might sell for $10 to $20, one with a Roger Federer or Rafael Nadal logo might go for $30 to $70, or even up to $100 if it's the same style one of them wore in a recent tournament: "If Roger Federer wore that same shirt in a tennis competition then it's going to command a premium. These are the nuances that you have to know when you are looking at items."

If you list an item that never sells, make a note of it and pivot. It's not the end of the world, he added: "Every single business and industry will produce items and release items that their customer base tells them, with their wallets, that they don't want. Ford will release a vehicle that doesn't live up to expectations and then discontinue the vehicle. They don't keep making the vehicle forever and expect a different outcome. They say, 'OK this was a failure.' Every single industry determines what's a good item, and what's not. We have to do the same thing in our industry."