Anyone can know the stat caps on any item ahead of time if they know the item level budgeting, stat weights, and how the general system works.

For example, for any given item level 70 accessory, most ratings (crit, accuracy, speed) cap out at 12, while the more expensive ratings cap out at 8 (determination) and 6 (piety). Base stat caps at 9, while Vitality (which is a little cheaper) caps at 10.