It varies depending on your game.

Sony Online Entertainment

SOE can allow as many accounts attached to one station account as you want. Many times we will see one account have an EverQuest, EverQuest 2, and Star Wars Galaxies account linked to one Station account. There are many more examples of this.

Unfortunately, we only give value on 1 account regardless if it has multiple accounts attached to one station account.

If you wish to receive more value for your accounts, we strongly recommend transferring your entire account to a brand new Station Account, and then selling 2 station accounts, rather than just one Station account.

Blizzard

World of Warcraft recently launched a BATTLE.NET option which you can merge your existing World of Warcraft Accounts to one BATTLE.NET account.

Unfortunately, we can only give value on just one account linked to one BATTLE.NET account.

If you wish to receive more value for your accounts, we strongly recommend contacting Blizzard support, and transferring one or more of the World of Warcraft accounts to a different BATTLE.NET account.

Please contact Blizzard@blizzard.com for more assistance.

PlayNC

PlayNC will allow you to attach a Aion, City of Heroes, City of Villains, Guild Wars, Guild Wars 2, Lineage 2, and Lineage 3 account to one PlayNC account.

Unfortunately, we can only give value on just one of those games, not all of them.

If you wish to receive more value for your accounts, we strongly recommend contacting PLAYNC support, and transferring one or more of the accounts to a different PlayNC master login account.

Funcom

Funcom will allow you to attach a Age of Conan and Anarchy Online account to one Funcom account.

Unfortunately, we can only give value on just one of those games, not both.

If you wish to receive more value for your accounts, we strongly recommend contacting Funcom support, and transferring one or more of the Age of Conan or Anarchy Online accounts to a different Funcom login account.