Legal/Allowed?

1. Trading stuff from one game to another game
2. Buying/selling cd-keys

1. That question cannot be answered with certainty because it depends on the respective end user license agreements (EULA).

2. Selling game accounts is prohibited in the Guild Wars EULA. It may or may not be acceptable to sell an unused CD key.

In both cases, I would not look at guildwarsguru.com as your potential selling platform.

I won't