In the end, it all comes down to training. Many companies offer training on composite inspection and repair. In addition, training is available on the different types of testing equipment mentioned. The more knowledgeable you are on inspection of composite structures and how to use the various inspection tools, the more comfortable you can be that the aircraft or component you are inspecting is airworthy.
High-tech tap tester
WichiTech's RD3 electronic digital tap hammer has taken composite tap testing to the next level. It uses an accelerometer in the head of the hammer that is hooked up to a computer to measure the response time of the hammer head. This is helpful in high noise environments since the user does not need to hear the sound, the hammer itself measures it and provides a numerical display.