People getting around games ToS' will always be a thing - since Runescape is the example being used, it is expressly banned to both purchase and sell gold coins. This is not a problem exclusive to MMOs, it's a problem with any game with a leveling system, currency, or items that are tradable between players.
Examples: FIFA packs, Runescape/MMO gold, League of Legends accounts/boosts (names as well) , Valorant accounts/boosts, CS:GO items (names, accounts and boosts as well), Neopets items and gift boxes, Diablo 3 boosts/accounts, and on and on...
Examples: FIFA packs, Runescape/MMO gold, League of Legends accounts/boosts (names as well) , Valorant accounts/boosts, CS:GO items (names, accounts and boosts as well), Neopets items and gift boxes, Diablo 3 boosts/accounts, and on and on...