I was trying out the guild tax, to see what it does, but apparently it does absolutely nothing.

I don't know what its meant to do, so I wouldn't know.

It's supposed to tax all members a certain percentage of the money they earn from NPC attacks. As far as I know, it doesn't tax winnings from PVP.

I was attacking NPC's and it didn't tax me anything when I set the value to 70%.

I believe this is a feature that was used primarily in the infamous Round 3. Probably hasn't worked since then, just no one really tried to use it.

Thought the tax applied to PvP kills.

 I could have sworn we'd replaced that with something useful. I'll sort it out