A good place to buy a game account is.
https://www.playerauctions.com/about/buy-game-accounts/
When buyers and sellers reach an agreement, PlayerAuctions receives the payment and holds it until the buyer verifies that he received the goods.
The company's fees vary, but generally they run about 10 percent of the transaction amount.
There are many websites that act as a marketplace for trading game accounts (e.g. playerup.com, playerauctions.com, g2g.com, epicnpc.com).
If possible, it is advisable to deal face-to-face as it offers a sense of security for both sides.