There is a way to. OSRS Gold is sourced by "less-than reliable" means botting, fraud and account theft, and is then "delivered" directly to the purchaser through a different account. There is also the possibility of being taken advantage of or even being reported for fraud since this can be considered "real-world dealing" and dropping or picking up, or the transfer of a huge amount of gold at once can appear... like a scam.
BTW, "real-world trading" is against the rules of Runescape and Jagex will beg you to clap. The only way you can "buy gold" is to pay real money for an Bond (an item that Jagex actually sells) and selling it to a different player in exchange for gold that is available in the game.