You can appraise common or well-known objects with a DC 12 Appraise check. Failure means that you estimate the value at 50% to 150% (2d6+3 times 10%,) of its actual value.
Appraising a rare or exotic item requires a successful check against DC 15, 20, or higher. If the check is successful, you estimate the value correctly; failure means you cannot estimate the item's value.
A magnifying glass gives you a +2 circumstance bonus on Appraise checks involving any item that is small or highly detailed, such as a gem. A merchant's scale gives you a +2 circumstance bonus on Appraise checks involving any items that are valued by weight, including anything made of precious metals.
These bonuses stack.
Action: Appraising an item takes 1 minute (ten consecutive full-round actions).
Try Again: No. You cannot try again on the same object, regardless of success.
Special: A dwarf gets a +2 racial bonus on Appraise checks that are related to stone or metal items because dwarves are familiar with valuable items of all kinds (especially those made of stone or metal).
The master of a raven familiar gains a +3 bonus on Appraise checks.
A character with the Diligent feat gets a +2 bonus on Appraise checks.
Synergy: If you have 5 ranks in any Craft skill, you gain a +2 bonus on Appraise checks related to items made with that Craft skill.
Untrained: For common items, failure on an untrained check means no estimate. For rare items, success means an estimate of 50% to 150% (2d6+3 times 10%).
The character can sense magical auras in objects.
Detect Magic: The character can sense if an item has a magical aura. He or she can then use Spellcraft to learn more about the item as if he or she had already cast detect magic on the item. This requires a full-round action.
Source: SRD 3.5 Combined Skills