1. Determine the type of gemstone tester you need. Gemstone testers come in a variety of types, including electronic testers, acid testers, and refractometers. Consider the type of gemstones you will be testing and the accuracy you need.

2. Research the different brands and models of gemstone testers available. Read reviews and compare features to find the best tester for your needs.

3. Purchase the gemstone tester from a reputable dealer. Make sure the dealer offers a warranty and a return policy in case the tester does not meet your expectations.

4. Follow the instructions provided with the tester to ensure proper use and maintenance.

5. Store the tester in a safe place when not in use.