For the most part, a reputable jeweler will not risk their longstanding reputation for short term gain. However, to ensure that your diamonds are not swapped when leaving them at a shop you should request to have each gem 'plotted out'. Plotting is when a jeweler maps out any inclusions in the gem which is unique to each one. You will want a copy of plot for yourself and one for the jeweler. If the jeweler does not agree to plotting, then I recommend they be taken elsewhere. Again, for the most part, diamond switching is not rampant.
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