Items come in many different qualities which can have different effect their use and durability, unless an item is specifically noted to be of a certain quality it is considered to be common quality.
Poor Quality
A poor quality item has a base -1 to its use and breaks if it is hit with a critical attack, fumbled with a skill/ability check or fails a saving throw. A poor item usually costs half as much as a normal quality item.
Common Quality
No effect.
Masterwork Quality
A masterwork item has a base +1 to one of its properties/abilities (eg. +1 to hit or damage for a weapon, +1 to AC for armor or +1 to skill rolls for tools) and +2 to its item saving throws. A masterwork item usually costs 10 to 50 times as much as a normal quality item.