Fortnite is a free-to-play game, yet some players are spending thousands of dollars on it.

The popular battle royale-style game is posting record revenue every month. Fortnite made $300 million in April, according to gaming research firm SuperData.

Players exchange real money for in-game currency called v-bucks. Gamers use v-bucks to buy new skins, accessories and emotes for their avatars. Fortnite developer Epic Games offers different character skins almost every day, causing some players to miss out on some cosmetic upgrades.

Gamers can also buy Fortnite accounts and services on unofficial marketplaces like eBay. Sellers use the online marketplace to auction accounts fully loaded with skins, emotes and accessories. Once a deal is reached, sellers complete the sale by giving the buyer the email and password attached to an advertised account.

While some players will shell out thousands on purely cosmetic purchases, others may choose to spend on sharpening their skills or at least padding their stats.

Players can also find coaching sessions on these marketplaces for about $20 an hour. Others offer to log into the buyer's account to boost their stats in exchange for cash. These auctions can range from $3 to $6,000.