A promotional image of online flea market Danggeun Market / Courtesy of Danggeun Market

Top sellers at online flea markets are earning more than 200 million won ($149,900) each per year amid steeply growing demand for used goods over persistent inflation, according to data, Monday.

Compiled by the National Tax Service (NTS), the data released by Rep. Park Sung-hoon of the ruling People Power Party showed that the combined sales of the top 10 vendors across all secondhand trading platforms in Korea totaled 2.25 billion won for 2023.

"In other words, each of the 10 posted sales averaging 225 million won over the cited period," the lawmaker said.

The finding came as online secondhand marketplaces began in the form of small internet communities in the early 2000s and have since evolved into a broad range of smartphone app-based platforms.

These platforms included the four major market players — Danggeun Market, Bungaejangter, Joonggonara and HelloMarket.

According to the NTS, an estimated 525 sellers in the secondhand market in 2023 were believed to professional traders — unlike most of the users.

Each of the 525 posted sales averaging 43.4 million won last year, which is equivalent to the annual salary of many regular workers in the country.

The tax agency noted that these traders accordingly were liable to pay comprehensive income tax.

The tax is on all types of income combined, and is applicable to individuals earning income beyond wages, such as from financial investments, rental properties and private businesses.

Park called on the NTS to "closely monitor the traders on the secondhand markets to prevent tax evasion and other breaches of the tax law."

He said, "The tax agency also should make efforts that no innocent user is victimized by any attempted exploitation of the markets."