All Dwarves are Greedy. But no Dwarf Clan is as greed as the evil Deep Dwarves. Their greed lead them to break the Codex and dig deep into the Elder Earth. And pay they did.
Still Greed rules their small hearts, and so they are expert Hagglers.
A small bonus to a Race that is in all inferior to Dwarves.
Idea: Give Duergar Racial Haggle. Automastered. And perhaps 103%. 
Agreed.
Very Nice.
Inferior? I would put duergar cleric against dwarf cleric anyday.
That'd be alike belting your head against a brick wall for both parties, wouldn't it?
Inferior? I would put duergar cleric against dwarf cleric anyday.
And that proves what exactly? 
Religion choices have nothing to do with the fact that dwarf stats are better than duerger stats.
Do Duergars have berserk mastered like Dwarves?
Do Duergars have berserk mastered like Dwarves?
Yes
I think duergar could use a +1 or +2 con.
Sitting at 22 when dwarves are 25? Big gap there.
They should have not dug so deep.
Any way they still have +2 DEX and same STR on Dwarves.
That makes them better at meele. If it was not the huge HP difference. A Dwarf get like +20% HP on a Duergar.
I think Con from 22 -> 23 would aid with this.
And remember, Duergar can burrow.