Just started the game yesterday and liking it so far. But confused about this: some weapons come with “-X dps if equipped”. What good is a weapon that does negative damage? Makes no sense to me. Been avoiding anything with that so far. Good idea? Bad idea?
The stat is relative to your current equipped weapon. It won’t do negative damage, it will just do less than what you’ve got.
Depending on your build, the dps stat is irrelevant (or, rather, inaccurate). This is particularly the case for casters.
What weapon to use is based on your build.
Most the time with melee toons i prioritize attack speed over whether or not it says -x or +x dps because of proc or weapon pool skills.
Casters i use weapons as a stat stick, mostly just looking for flat and higher % values for the dmg type i deal and not worrying about how much dmg i hit them for with my twig. 
Thanks, guys. Will keep that in mind. Still seems strange to me, though. But I can live with it.
Its just a comparison between two dps.
Imagine the weapon you’re using allows you to reach 1000 dps.
Then, you find two weapons: the first would allow you to reach 1100 dps and the second 950 dps.
The tooltip on the first will show +100 dps (1100 - 1000) and the tooltip on the second will show -50 dps (950 - 1000).
With the second, you’re loosing 50 dps so you go from 1000 to 950 and not from 1000 to -50. You don’t get to do negative damages.
It’s an indicator to do a quick comparison between two weapons.
It can help but it’s not absolute comparison as other factors can enter for your choice of weapon.
So that’s how it works. Cool. Makes sense now. Thanks much, Peredur.
Wow, that’s great info! Just lurking here. 
Thanks!