I don't own those games so I can't comment on them, but I'll give you some general advice.
It was a good thing to ask here about them. A lot of games, especially multiplayer-focus ones, have systems where you have to associate a CD-key with an account, which removes the CD-key out of circulation afterward (Battlefield 2, Guild Wars, etc.).
Unless you know exactly the type of copy-protection/registration system a game is using, you should ask others what they use, then decide how to proceed from there.
If a game is using a system that binds a cd-key to a single account, such as Guild Wars, make sure to ask the seller whether the key has been used or if they will be including the created account (against most EULAs, so watch it). Also watch it with games like Blizzard's titles, where a key can be used on more than one account, but only one player-per-key can be online at any time.