It's a phrase I hear every day, yet, rarely is there a simple answer.
First, it is my job to find out what market level my client is referring to. What it's worth on ebay can be very different to what it sells for at a fine jewelry store in a high rent district. So before I can give them the magic number I must ask the following questions:
1/ What will you do with the appraisal?
For example, do you need to buy insurance coverage in case it is lost or stolen. Or, do you plan to donate the jewelry to a charity and need the appraisal to make a tax deduction? Maybe you and your siblings inherited some jewelry and need an appraisal to equitably divide the pieces. These three examples can easily result in three different value conclusions.
2/ If you are selling the jewelry, how much time do you have?
The value of jewelry that needs to be sold in three days (forced liquidation) will be much lower than the value of jewelry that can be sold at leisure.
3/ Do you have any accompanying Lab reports?
For example, a report from a trade respected Laboratory such as the GIA, AGL, AGS or Gubelin, confirming origin of color in a Burmese ruby and no indications of treatment, can have a significant impact on its value.
4/ Does the jewelry have any provenance?
For example, do you have documentation proving the jewelry was from the estate of Marilyn Monroe? Provenance can add value to the piece if the previous owner was particularly famous and the current generation of jewelry buyers can still remember the person.
There are many other factors affecting value of jewelry and watches and these are determined on a case-by-case basis. The professional appraiser should carefully evaluate the pieces to identify the type of metal, type and quality of fabrication, diamond/gemstone measurements, weight estimation and grading, hallmarks, trademarks, signatures, condition, period and desirability in the market place. Then, finally after some research that simple question can be answered.