Well i saw alot of guys speaking about the grade of weapons, naming their bazar with weapon grade and in the weapon too. But actualy i and my friends don't even know WTF thoes this grade mean or for what porpuse it his since it can be upgraded for high price. Can anyone spend his times explaining this to me since the game doesn't provide any help about it? Thanks.

Weapon grade determines the weapons attack and Durability. So same weapons with different grades would have higher or lower attack and durability.

if you compare two of the same weapon with the same level, the one with higher grade quality shows a difference attack power. This is especially more apparent when you compare a weapon with grade 1 quality to a weapon with grade 30 or higher.