Why would this be wrong at all? If that is how he/she wants to play - what does that really matter to anyone?
If you feel he/she should be participating in .9x or swaps - than make it mandatory - otherwise, leave them alone to their own devices.
If this player does not see the advantage of the guild .9x/swap, then they may be losing out and paying more to level their own GBs. On the other hand, he/she may be participating in a lucrative deal outside of the guild. Why do you really think you should be in some kind of position to control how a fellow guildie decides how to level up their GBs?